Yamaha XS650 backfire
Dave
overdue). By the time I finished it was pretty dark in my garage, so I
couldn't help but notice that the left cylinder was backfiring... I could
see the blue flame inside the left muffler. My old rusty pipes were so
friggin' loud that the backfire may have been present last year, I'm just
not sure. What might cause this? I swapped the plugs between L & R
cylinders, but the backfire stayed on the left (damn!). The bike seems to
rev up okay, could it possibly just be an adjustment of my air mixture
screw? I'll throw a tachometer on the left plug lead tonight just to make
sure I'm getting spark.
Dave
¿
> �The bike seems to
> rev up okay, could it possibly just be an adjustment of my air mixture
Maybe your carbs are getting a little plugged up inside. You might try
adding a few ounces of Berryman B12 Choke and Carburetor Cleaner to a
full tank of gas and going for a slow ride to clean out the idle
circuits.
There are two kinds of backfires related to dirty carbs. One is the
loud *bang!* associated with high fuel levels caused by dirty float
valves.
The other kind of backfire is a wimpy *piffle-piffle-snap!* on
deceleration, That's caused by dirty idle jets and passages.
Dave
"�" <macm...@gmail.com> wrote in message
news:d8519415-1757-47bf...@z19g2000vbz.googlegroups.com...
On Jun 9, 11:09�am, "Dave" <dspear9...@yahoo.com> wrote:
>> �The bike seems to
>> rev up okay, could it possibly just be an adjustment of my air mixture
>Maybe your carbs are getting a little plugged up inside. You might try
>adding a few ounces of Berryman B12 Choke and Carburetor Cleaner to a
>full tank of gas and going for a slow ride to clean out the idle
>circuits.
>
>There are two kinds of backfires related to dirty carbs. One is the
>loud *bang!* associated with high fuel levels caused by dirty float
>valves.
>
>The other kind of backfire is a wimpy *piffle-piffle-snap!* on
>deceleration, That's caused by dirty idle jets and passages.
I'll try carb cleaner, I've got a bottle someplace, I recall I ran some
through last year or the year before. The other cylinder runs fine. I
think I'm going to end up pulling these carbs apart anyways at some point.
I would think that a plugged air jet might cause backfiring at idle, but I
really haven't worked on carbs enough to know...
¿
> I would think that a plugged air jet might cause backfiring at idle, but I
> really haven't worked on carbs enough to know...
If you're fairly sure that the air jet has gotten plugged up, a shot
of aerosol carb cleaner would easily clean it out.
I buy both types, B12 in aerosol form and B12 in the handy liquid form
for adding to the gas tank.
Many Japanese ignition systems will fire both spark plugs at the same
time, using one sensor or one set of points to trigger the ignition.
When you have a waste spark firing, you'll hear rumbles in the exhaust
pipe on deceleration and you'll also get backfires when the carbs are
dirty because unburned mixture will build up in the exhaust pipe over
two or three exhaust strokes.
The Older Gentleman
> What might cause this?
Incorrect mixture. Incorrect timing (I am not sure if the 1980 model XS
had points or electronic ignition, and I cba to check right now).
--
BMW K1100LT Ducati 750SS Honda CB400F & XBR500 Triumph Street Triple
Suzuki TS250ER
If you don't know what you're doing, don't do it. And RTFM.
chateau dot murray at idnet dot com
The Older Gentleman
> Many Japanese ignition systems will fire both spark plugs at the same
> time, using one sensor or one set of points to trigger the ignition.
But the XS650 *doesn't*.
¿
Turd) wrote:
> � <macmi...@gmail.com> wrote:
> > Many Japanese ignition systems will fire both spark plugs at the same
> > time, using one sensor or one set of points to trigger the ignition.
>
> But the XS650 *doesn't*.
Well, take the time to *look it up*, you silly cunt.
BTW, I'm a cracker. Eat me.
The Older Gentleman
> > But the XS650 *doesn't*.
>
> Well, take the time to *look it up*, you silly cunt.
Don't need to. I've rebuilt two.
But carry on posting erroneous information if you want to.
Dave
"The Older Gentleman" <totallyde...@yahoo.co.uk> wrote in message
news:1j12esf.46eyv416hc4ydN%totallyde...@yahoo.co.uk...
> Dave <dspea...@yahoo.com> wrote:
>
>> What might cause this?
>
> Incorrect mixture. Incorrect timing (I am not sure if the 1980 model XS
> had points or electronic ignition, and I cba to check right now).
The XS650G (1980) has electronic ignition, timing cannot be adjusted.
As for incorrect mixture, I'll try re-setting the air mixture screw on the
problem side for best idle although last time I used the "dead cylinder"
method I had quite a time just keeping the bike from stalling. I added some
carb cleaner and went for a spin last night, the bike runs just fine at
higher than idle rpm's.
Thanks.
Dave
¿
> "The Turd That Won't Flush" <totallydeadmail...@yahoo.co.uk> wrote in messagenews:1j12esf.46eyv416hc4ydN%totallyde...@yahoo.co.uk...
> > Incorrect mixture. Incorrect timing (I am not sure if the 1980 model XS
> > had points or electronic ignition, and I cba to check right now).
>
> The XS650G (1980) has electronic ignition, timing cannot be adjusted.
Yes, and it only has *one* timing sensor and a 360 degree crankshaft,
so
both coils have to fire at the same time. One of the sparks is wasted
because the exhaust valve on that cylinder is open.
If there is a buildup of unburned mixture in the exhaust pipe on that
side, you'll hear a bang! out of that cylinder when the plug fires.
I advise you not to waste a lot of time debating with "The Turd That
Won't Flush". He loves to debate and argue instead of helping riders
find solutions to their problems.
Before you know it, he'll have you apologizing to him and thanking him
for giving you a ration of shit.
> As for incorrect mixture, I'll try re-setting the air mixture screw on the
> problem side for best idle although last time I used the "dead cylinder"
> method I had quite a time just keeping the bike from stalling. �I added some
> carb cleaner and went for a spin last night, the bike runs just fine at
> higher than idle rpm's.
OK, just remember that you can adjust the idle mixture screw all day
and it won't change a thing if the idle jets and air jets and passages
are plugged up with gum and varnish from evaporated gasoline.
Dave
>
>OK, just remember that you can adjust the idle mixture screw all day
>and it won't change a thing if the idle jets and air jets and passages
>are plugged up with gum and varnish from evaporated gasoline.
Yeah, I'm just hoping. I don't really want to pull & clean the carbs if I
don't have to.
The Older Gentleman
> The XS650G (1980) has electronic ignition, timing cannot be adjusted.
It'll be the carb, then.
The Older Gentleman
> "�" <macm...@gmail.com> wrote in message
If they're really gummed, then all the magic snake oil in the world
won't help. Ultrasound cleaning works wonders. I used it on a carb for
an old Honda 125 single last year: brilliant.
Generally, carbs only get bunged up if they've been left for a long,
long time (like well over a year). In a hot climate, obviously, the fuel
inside them will evaporate and gum them up in less time than that.
If the bike hasn't been standing for ages, then it's not going to be
gummed carbs anyway, but just bad adjustment.
Mark Olson
>
> "ￜ" <macm...@gmail.com> wrote in message
I recently bought a 1984 VF500F that wouldn't run unless I had the enrichener
lever turned all the way on. I tried B-12, Yamaha Carb Cleaner, etc. I took
the mixture screws out and sprayed B-12 through the passageway. Nothing really
helped except removing the carbs and poking a soft copper wire strand (really
fine and really soft) through the pilot jets. 2 of the 4 pilot jets were
completely blocked, the other two partially blocked. When those little jets
are fully blocked, no fuel system cleaners are likely to do anything because
none of it actually flows through the jet. If the jets are only partially
plugged then you have a chance of cleaning them out chemically.
You are dealing with an engine that has carbs that are relatively easy to
remove & replace, plus there are only two of them. Stop putting it off and
pull the carbs. Only take apart one at a time, take your time, do not, I repeat
do not adjust the floats unless you are *sure* they are misadjusted, just remove
all the jets, the idle mixture screws, and run a shitload of spray carb cleaner
through everything. Especially make sure the idle circuit, idle mixture port,
and the transition ports all are totally unblocked.
Avoid getting carb cleaner on the diaphragms, it generally
won't really hurt anything but until they dry out they will swell up a lot and
you'll have a hell of a time getting them to fit. Also make sure you don't
lose the little washer, spring, and tiny O-ring on the mixture screws. I like
to work with an old towel on top of my workbench to catch little parts and keep
them from skittering off into oblivion. Sometimes there are tiny O-rings between
the diaphragm covers and the top of the carbs, keep a sharp eye out when you're
taking that apart too.
If you don't have an official Yamaha manual, try and get your hands on one, if
you can't or aren't willing to pay for one, at least get a Clymer or Haynes
manual or google for a diagram that shows where all the little passages in the
carbs go. Despite what I said about not touching the floats, you definitely
need to check the float height before putting the carbs back together. It's
really nice to be able to check the actual fuel level with the carbs assembled
but getting the float level correct is good enough 99% of the time.
Good luck.
Dave
"Mark Olson" <ols...@tiny.invalid> wrote in message
news:95idnVT5j4kvbrLX...@posted.visi...
>
> You are dealing with an engine that has carbs that are relatively easy to
> remove & replace, plus there are only two of them. Stop putting it off
> and
> pull the carbs.
Deep down I already knew this. I'll try to fit it in on the weekend. It's
just such a pain in the you know where to adjust and balance them. I've got
to take it out for some highway rides and start the painful guess 'n check
process of re-jetting for my new exhaust, so the carbs will be coming off
anyways, one more time won't kill me.
>
> If you don't have an official Yamaha manual, try and get your hands on
> one,
I've got the manual, it's available online for free. Thanks for your
advice.
Dave
The Older Gentleman
> When those little jets
> are fully blocked, no fuel system cleaners are likely to do anything because
> none of it actually flows through the jet. If the jets are only partially
> plugged then you have a chance of cleaning them out chemically.
Listen to this man. He speaks the truth. Lots of people put their faith
in all these magic potions and cures, but ultimately, fixing something
properly is the only sure way.
¿
Won't Flush) wrote:
> Listen to this man. He speaks the truth. Lots of people put their faith
> in all these magic potions and cures, but ultimately, fixing something
> properly is the only sure way.
Do NOT listen to The Turd That Won't Flush. He's more interested in
proving himself to be "right" (by his own rules) that he cannot accept
that there are quick fixes to simple problems by using inexpensive
chemicals designed to cure such problems.
I go through this business of plugged up carburetors *every* spring
when I take the motorcycles out of winter storage, and the idle jets
are seldom as plugged up
as Mark Olson suggests, but the engine stalls, won't idle, or
backfires.
¿
> Deep down I already knew this. I'll try to fit it in on the weekend. It's
> just such a pain in the you know where to adjust and balance them. I've got
> to take it out for some highway rides and start the painful guess 'n check
> process of re-jetting for my new exhaust, so the carbs will be coming off
> anyways, one more time won't kill me.
Steer clear of Dynojet kits. Dynojet is trying to enhance their bank
account by keeping speed secrets *secret*.
I recommend going to www.factorypro.com and studying what they have to
say about jetting CV carburetors. The owner of Factory Pro is *not*
trying to keep secrets, he's telling how to rejet a carburetor using
stock Mikuni or Keihin parts.
Your carbs are probably made by Hitachi, but Mikuni main jets should
fit just fine.
The problem with re-jetting is that most home mechanics do not
understand how the size #'s relate to orifice area.
Since I've explained this concept dozens of times in this NG, I won't
go into it again, but you can google up "round jet" and find the
information.
The Older Gentleman
>Steer clear of Dynojet kits. Dynojet is trying to enhance their bank
>account by keeping speed secrets *secret*.
Nonsense
>
> Your carbs are probably made by Hitachi,
Mikuni, actually.
You really are preaching from a position of ignorance here.
The Older Gentleman
> I go through this business of plugged up carburetors *every* spring
> when I take the motorcycles out of winter storage
Which raises the question: why don't you just drain the carbs before
storing the bike?
¿
Gentleman)
> Which raises the question: why don't you just drain the carbs before
> storing the bike?
Inaccessability of drain screws behind fairings, gas tanks, etc.
Easier to add B12 to gasoline and ride the carbs clean.
Alphonse Q Muthafuyer
>I started up my 1980 XS650G last night after fitting new mufflers (long long
>overdue). By the time I finished it was pretty dark in my garage, so I
>couldn't help but notice that the left cylinder was backfiring... I could
>see the blue flame inside the left muffler.
Additional detail might be helpful.
Intermittent blue flame? How intermittent?
Does the left header pipe heat up at a different rate than the right?
Any chance you could've burned an exhaust valve?
Lots of other possibilities ...
AQ
"The monkey and the baboon was playing 7-up.
The monkey won the money but he scared to pick it up.
The monkey stumbled, mama.
The baboon fell.
The monkey grab the money and he run like hell!"
- from "Dirty Motherfuyer", Roosevelt Sykes, around 1935
The Older Gentleman
So just shut off the fuel, drain the tank, whatever. It's what I do on
my old Honda and I *never* have a gummed carb problem, despite sometimes
leaving the bike for six months.
--
BMW K1100LT Ducati 750SS Triumph Street Triple Honda XBR500 CB400F
SH50 MZ TS250 GHPOTHUF1 chateaudotmurrayatidnetdotcom
Nothing damages a machine more than an ignoramus with a manual, a
can-do attitude and a set of cheap tools
¿
Gentleman) wrote:
> ¿ <macmi...@gmail.com> wrote:
> > Easier to add B12 to gasoline and ride the carbs clean.
>
> So just shut off the fuel, drain the tank, whatever.
The fuel is automatically shut off when the vacuum-operated petcock
closes or the electric fuel pump stops. The float bowls are
inaccessible without removing the gas tank.
Draining the gas tank is impossible without unbolting it, and draining
the tank just invites internal rust.
What I do is add a few ounces of gasoline stabilizer to a full tank of
gas and idle the egine for a while to get it into the carbs.
> It's what I do on
> my old Honda and I *never* have a gummed carb problem, despite sometimes
> leaving the bike for six months.
It's a lot cooler where you live. It gets up to 100 degrees F every
day during the summer around here. My carbs may gum up in a matter of
weeks if I don't have time to ride.
The Older Gentleman
> On Jun 11, 2:47 am, totallydeadmail...@yahoo.co.uk (The Older
> Gentleman) wrote:
> > � <macmi...@gmail.com> wrote:
> > > Easier to add B12 to gasoline and ride the carbs clean.
> >
> > So just shut off the fuel, drain the tank, whatever.
>
> The fuel is automatically shut off when the vacuum-operated petcock
> closes or the electric fuel pump stops.
That's a problem, sure enough.
>The float bowls are
> inaccessible without removing the gas tank.
>
> Draining the gas tank is impossible without unbolting it, and draining
> the tank just invites internal rust.
Hm
>
> What I do is add a few ounces of gasoline stabilizer to a full tank of
> gas and idle the egine for a while to get it into the carbs.
>
> > It's what I do on
> > my old Honda and I *never* have a gummed carb problem, despite sometimes
> > leaving the bike for six months.
>
> It's a lot cooler where you live. It gets up to 100 degrees F every
> day during the summer around here. My carbs may gum up in a matter of
> weeks if I don't have time to ride.
That's certainly different weather conditions. I'd do something like fit
an inline manual tap or similar. Some form of shut-off. Then just run
the engine until it's starved of fuel from the carb float bowls.
FI engines are a different kettle of fish of course.
Dave
"Alphonse Q Muthafuyer" <mutha...@gmail.com> wrote in message
news:e6f035piel6514ajj...@4ax.com...
> On Tue, 09 Jun 2009 18:09:43 GMT, "Dave" <dspea...@yahoo.com> wrote:
>
>>I started up my 1980 XS650G last night after fitting new mufflers (long
>>long
>>overdue). By the time I finished it was pretty dark in my garage, so I
>>couldn't help but notice that the left cylinder was backfiring... I could
>>see the blue flame inside the left muffler.
>
> Additional detail might be helpful.
>
> Intermittent blue flame? How intermittent?
Hmmm. I'd say about once every 1-3 seconds. Not regular though. flame..
flame.......flame.flame....flame...........flame.
>
> Does the left header pipe heat up at a different rate than the right?
I don't know but I will check this afternoon.
>
> Any chance you could've burned an exhaust valve?
>
I guess anything's possible. What actions on my part would lead to a burned
exhaust valve? Would a compression test tell me if I've got a bad valve?
The Older Gentleman
> I guess anything's possible. What actions on my part would lead to a burned
> exhaust valve?
Over-tightened (or neglected, which would produce the same effect) valve
clearances.
I still reckon it's mixture, though.
Alphonse Q Muthafuyer
>> Additional detail might be helpful.
>>
>> Intermittent blue flame? How intermittent?
>
>Hmmm. I'd say about once every 1-3 seconds. Not regular though. flame..
>flame.......flame.flame....flame...........flame.
The irregularity might be consistent with idle-jet problems.
>> Does the left header pipe heat up at a different rate than the right?
>
>I don't know but I will check this afternoon.
A truly cheap diagnostic. Just reach down and touch (before they get
too hot).
>> Any chance you could've burned an exhaust valve?
>>
>
>I guess anything's possible. What actions on my part would lead to a burned
>exhaust valve?
I likely should have said "warped", 'tho "burned" can be descriptive.
In a nutshell, abuse (i.e. over-revving a hot, hot engine, etc).
>Would a compression test tell me if I've got a bad valve?
Very likely. Got a tester handy?
Dave
>
> The irregularity might be consistent with idle-jet problems.
>
>>> Does the left header pipe heat up at a different rate than the right?
>>
>
Okay, left header pipe heats up WAY slower than right one. Threw a tach on
the lead, it's getting plenty of spark. Removed and sealed off port on
intake manifold where fuel petcock vacuum is taken off in case it's leaking.
No change.
>>> Any chance you could've burned an exhaust valve?
>>>
>>
>>I guess anything's possible. What actions on my part would lead to a
>>burned
>>exhaust valve?
>
> I likely should have said "warped", 'tho "burned" can be descriptive.
> In a nutshell, abuse (i.e. over-revving a hot, hot engine, etc).
>
>>Would a compression test tell me if I've got a bad valve?
>
> Very likely. Got a tester handy?
>
Compression is good ~115lb.
So I bit the bullet and removed, disassembled and cleaned the carbs. Tested
the diaphrams. I put new larger main jets in to compensate for my
aftermarket exhaust, I bought a few different sizes and will have to play
around with them to find the best one. I also was very pleased to note I
have the notched (adjustable) needles. These carbs did not seem in the
least bit dirty to me, and I have worked on some bad ones. On re-assembly I
happened to hold the completed assembly up to the light and huh? What's
this? I could see a fair chunk of light through the right (working) carb,
but the left side looks like a tight seal. Hmmm, that is very well likely
the problem all along. I rough-synched the carbs with drill bits, but by
then it was getting dark so I didn't get it all back together. Will report
back.
TOG@Toil
> So I bit the bullet and removed, disassembled and cleaned the carbs. Tested
> the diaphrams. I put new larger main jets in to compensate for my
> aftermarket exhaust, I bought a few different sizes and will have to play
> around with them to find the best one. I also was very pleased to note I
> have the notched (adjustable) needles. These carbs did not seem in the
> least bit dirty to me, and I have worked on some bad ones. On re-assembly I
> happened to hold the completed assembly up to the light and huh? What's
> this? I could see a fair chunk of light through the right (working) carb,
> but the left side looks like a tight seal. Hmmm, that is very well likely
> the problem all along.
Looks that way. Where's the light shining through? The carb/mounting
rubber joint or the mounting rubber/cylinder joint, or somewhere else?
If you want a weak mixture, having an ill-fitting carb will provide
it ;-)
Dave
"TOG@Toil" <totallyde...@yahoo.co.uk> wrote in message
news:fa88dad1-7b15-4603...@z14g2000yqa.googlegroups.com...
What I meant was that the idle adjust was set on the left (non-performing)
carb so that the throttle plate was 100% closed, whereas the right (idles
great) carb was adjusted via the synch screw to have a gap maybe 1 or even
1.5mm, allowing light end to end through the carb body. They were terribly
out of synch, with the idle set so one carb worked and one not so much.
I know all about ill-fitting carbs, cracked and/or leaking boots, poorly
sealing air boxes... problems like this seem to seek me out.
Dave
The Older Gentleman
> What I meant was that the idle adjust was set on the left (non-performing)
> carb so that the throttle plate was 100% closed, whereas the right (idles
> great) carb was adjusted via the synch screw to have a gap maybe 1 or even
> 1.5mm, allowing light end to end through the carb body. They were terribly
> out of synch, with the idle set so one carb worked and one not so much.
Easy fix, though.
--
¿
> Compression is good ~115lb.
If the compression ratio is only 8:1, cranking compression should be
about 117 psi, assuming that you live somewhere near sea level.
If the CR is 9:1, you should get about 133 psi after about five
compression cycles.
The Older Gentleman
Stock XS650 CR is closer to 9 than 8 to one, IIRC.
Anyway, it looks like he's already traced the problem.
Dave
"The Older Gentleman" <totallyde...@yahoo.co.uk> wrote in message
news:1j1qheb.6nkfzj1yzwhtjN%totallyde...@yahoo.co.uk...
>
> Anyway, it looks like he's already traced the problem.
>
> --
jets, new pilot jets. Squirted the be-jesus out of the carb passages with
cleaner. Bench-synched with drill bits. Fired it up last night and....
same symptoms. The bike will start and run with only the right plug
connected but not only the left (yes, I grounded a spare plug in the unused
plug lead to the block). With both plugs connected, right exhaust is warm,
sound is rhythmic bu-bu-bu-bu-bu-bu-bu-bu-bu-bu from right muffler. Left
exhaust is cool, backfires occur when I start it, last only about 30 seconds
or so, at least after 30 seconds I could no longer see blue flame in the
muffler. Sound is kind of a puh------puh-puh------puh----puh-puh-puh from
left muffler. Bike will NOT run on left cylinder only without throttle
opened up some. I can't help thinking that it's just not getting fuel
through the pilot circuit. Maybe I'm going to have to disassemble the left
carb enough to soak the carb body, I dunno.
So, I'm thinking to completely disassemble the carbs from each other and the
chunk of angle iron holding them together, switch them side for side, and
see if the problem moves. I did find out my fuel petcock leaks in the ON
position, so tonight I'll seal off the vacuum take-off on the left manifold
and see if that helps... I could test the compression in the right cylinder
too, but I'll wager that's about the same as the left... let's face it guys
it's a 29 year old bike with the original rings, I might not get 9:1 any
more.
Thanks for all the insight so far.
Dave
"�" <macm...@gmail.com> wrote in message
news:ea44fbd1-924c-48ac...@r31g2000prh.googlegroups.com...
> Compression is good ~115lb.
I live at 1,100 feet, so 9:1 shouldn't be too far off of my 115.
¿
> Ah, if only it were so easy. �So, I put it all back together. �New main
> jets, new pilot jets. �Squirted the be-jesus out of the carb passages with
> cleaner. �
Have you drilled out the EPA antitamper plugs in the sprues on top of
the carburetors, just forward of the diaphragm cap?
Refer to this drawing. Item #47 is a different part, but the line
points near the sprue I'm talking about. The anti-tamper plug is
probably made of brass and it is fairly thick.
Take a small drill and carefully drill a pilot hole in the anti-
tamper, then screw a small sheet metal screw into the pilot hole and
pull the screw and anti-tamper plug out with a pair of pliers.
Then, before removing the idle mixture screw, turn it in gently until
it just stops.
This may be as little as 1/4 to 1/2 a turn with the large pilot 42.5
pilot jets.
Write down the total number of turns or fractions of turns for each
idle mixture screw.
Then remove the idle mixture screws, being sure to save the small
spring, tiny washer, and tiny rubber o-ring.
Segregate the idle mixture screws, springs, washers, and o-rings as a
set, dedicated to each carburetor.
Then you can squirt Berryman B12 or any clear aerosol carb cleaner
handy into the hole the idle mixture screws came out of.
When you squirt carb cleaner into the #44 pilot air jet in the intake
of each carb, the cleaner should squirt freely out of the hole that
the idle screw came out of.
It should also squirt freely out of the #16 pilot jet and also squirt
freely out of a triangular pattern of three idle transition ports just
downstream of the throttle butterflies.
I find it necessary to reinstall the idle mixture screws and hold my
finger over the pilot jet orifice to get carb cleaner to flow freely
out of the 3 transition ports
when squirting it through the pilot air jets.
When you're ready to readjust the idle mixture screws back to the
factory settings, turn them clockwise gently, until they just stop,
then turn them back counterclockwise to the same number of turns that
you counted when you removed them.
http://webservices.motorsportdealers.com/parts/partImages/YAM/2/02/0758/0028.Gif
16 JET, PILOT (#42.5)
17 PLUG (rubber? It keeps fuel near the pilot jet orifice)
44 JET, AIR PILOT (#135.0)
¿
> I live at 1,100 feet, so 9:1 shouldn't be too far off of my 115.
The geometric compression ratio of 9:1 does not change with altitude,
but
the ambient air pressure does change, it's about 3.6% lower on a
Standard Day which is 59 degrees F, sea level, dry air.
If you're curious about what I'm talking about, google for "ICAO
Standard Atmosphere Table".
Air density at 1100 feet and 59 degrees is about 2.9% lower than at
sea level.
Air density at higher temperature than the standard 59 degrees F has
even more effect than altitude change.
If you're doing your compression tests in 90 degree ambient air
temperature you can expect the readings to be lower than what's
specified in a factory manual that assumes you're doing the test in
Tokyo on a nice cool day.
TOG@Toil
> "The Older Gentleman" <totallydeadmail...@yahoo.co.uk> wrote in messagenews:1j1qheb.6nkfzj1yzwhtjN%totallyde...@yahoo.co.uk...
I doubt it's a compression problem. As you appear to have surmised,
engine wear is usually consistent on both/all pots unless something
fairly nasty has happened.
Fuel tap? Doubt it, but you could try running the thing with the tap
on the Prime setting, just to be sure.
The best thing to do is probably to have the carbs ultrasonically
cleaned. It's not expensive and it works - I've had it done.
Ultrasound dislodges all the little bits of crap and varnish that
soaking won't get (nor will the proprietary snake oil). Or get a
decent set of used carbs, clag those on and see what happens. I had to
do that too, a few years ago, when I was restoring an old Honda CB500T
whose carbs (as it turned out) were really beyond hope.
By the way, the 500T wasn't worth restoring, but I just felt perverse.
I wound up with a fine example of an utterly dreadful motorcycle.
frijoli
>
> By the way, the 500T wasn't worth restoring, but I just felt perverse.
> I wound up with a fine example of an utterly dreadful motorcycle.
I went to a car show once and there was a restored Pacer.
Your statement made me laugh and remember that.
Clay
TOG@Toil
I've seen pictures of the Pacer. Even thought it looked quite good, in
a distinctive sort of way. What was so bad about it?
<Thinks>
Hang on, while I switch off my binary filter.
Dave
"frijoli" <c...@dud.gov> wrote in message
news:h1sts6$j73$1...@news.eternal-september.org...
Wow, haven't though of Pacers in years... there was a house on my paper
route when I was about 14 that had TWO of them, his 'n hers, in the
driveway... owners were very proud of them. In a freakish sort of way.
>
> Clay
Timo Geusch
You could start here: http://en.wikipedia.org/wiki/AMC_Pacer
The UK import story is quite, err, interesting...
Mind you, with a 4L out of a 90s Jeep it might are work reasonably well.
--
Morini Corsaro 125 | XL250 Motosport | R1150RT
Laverda SF2 | Harley FXD BOTAFOF #33 TWA#10
The UKRM FAQ: http://www.ukrm.net/faq/index.html
"Je profite du paysage" - Joe Bar
The Older Gentleman
> TOG@Toil wrote:
>
> > >
> >
> > I've seen pictures of the Pacer. Even thought it looked quite good, in
> > a distinctive sort of way. What was so bad about it?
> >
> > <Thinks>
> >
> > Hang on, while I switch off my binary filter.
>
> You could start here: http://en.wikipedia.org/wiki/AMC_Pacer
>
> The UK import story is quite, err, interesting...
Isn't it, just? What an amazing lash-up.
>
> Mind you, with a 4L out of a 90s Jeep it might are work reasonably well.
You mean, drink even more fuel and go even slower?
¿
wrote:
> You could start here:http://en.wikipedia.org/wiki/AMC_Pacer
Well, there goes the neighborhood. Next we'll see Ivan Reid confessing
a predilection for Humbers in a thread about XS650 fart-bangs...
Timo Geusch
> Timo Geusch <tnewsSP...@unixconsult.co.uk> wrote:
>
> > TOG@Toil wrote:
> >
>
> > > >
> > >
> > > I've seen pictures of the Pacer. Even thought it looked quite
> > > good, in a distinctive sort of way. What was so bad about it?
> > >
> > > <Thinks>
> > >
> > > Hang on, while I switch off my binary filter.
> >
> > You could start here: http://en.wikipedia.org/wiki/AMC_Pacer
> >
> > The UK import story is quite, err, interesting...
>
> Isn't it, just? What an amazing lash-up.
> >
> > Mind you, with a 4L out of a 90s Jeep it might are work reasonably
> > well.
>
> You mean, drink even more fuel and go even slower?
Na, same fuel consumption, roughly twice the power.
¿
wrote:
> > You mean, drink even more fuel and go even slower?
>
> Na, same fuel consumption, roughly twice the power.
And what, precisely is the fuel consumption of an AMC/Jeep 4.0 liter
engine?
A local woman was offering to trade her Jeep Grand Cherokee for
*anything* that would save gas last summer, during the height of the
price gouging, because she had to haul her kids to school and back 10
times a week.
The Wikipedia article also claims that the AMC/Jeep 4.0 liter engine
will go 300,000 miles between overhauls, which is double the
expectancy of the 3.7 liter V6 used in the Jeep Liberty models from
about 2001 on...
The 3.7 Liberty gets 22 mpg on the highway and about 16~18 mph in
town.
Dr Ivan D. Reid
Humbers? I think a neighbour had a Super Snipe when I was five or
so. Cars weren't too numerous in our neck of the woods at that time.
--
Ivan Reid, School of Engineering & Design, _____________ CMS Collaboration,
Brunel University. Ivan.Reid@[brunel.ac.uk|cern.ch] Room 40-1-B12, CERN
GSX600F, RG250WD "You Porsche. Me pass!" DoD #484 JKLO#003, 005
WP7# 3000 LC Unit #2368 (tinlc) UKMC#00009 BOTAFOT#16 UKRMMA#7 (Hon)
KotPT -- "for stupidity above and beyond the call of duty".
Rob Kleinschmidt
> So, I'm thinking to completely disassemble the carbs from each other and the
> chunk of angle iron holding them together, switch them side for side, and
> see if the problem moves. I did find out my fuel petcock leaks in the ON
> position, so tonight I'll seal off the vacuum take-off on the left manifold
> and see if that helps... I could test the compression in the right cylinder
> too, but I'll wager that's about the same as the left... let's face it guys
> it's a 29 year old bike with the original rings, I might not get 9:1 any
> more.
I think I'd test the compression just because it's
an easy test if you're eliminating suspects. I like
the idea of the carb swap too.
Rob Kleinschmidt
Compared to the AMC Gremlin, I always thought
the Pacer was a thing of beauty. (sort of).
Dave
"Rob Kleinschmidt" <Rkleinsc...@aol.com> wrote in message
news:336089fb-ee12-4128...@y4g2000prf.googlegroups.com...
I like the idea of the compression test better than the carb swap... 2
minutes vs. 1 hour. What the hell, I'll test it. Swapping the carbs looks
to be a bit of a whore, I'm not sure if they're actually identical... one's
got the idle-adjust screw on it and I don't think there's a tab for that on
the other one. I might be wrong. Other than that I think everything could
be swapped, I'd need to exchange throttle plate rods I think to get the
fittings in place for the throttle cable and throttle plate linkage.
Mark Olson
>> I think I'd test the compression just because it's
>> an easy test if you're eliminating suspects. I like
>> the idea of the carb swap too.
>
> I like the idea of the compression test better than the carb swap... 2
> minutes vs. 1 hour. What the hell, I'll test it. Swapping the carbs
> looks to be a bit of a whore, I'm not sure if they're actually
> identical... one's got the idle-adjust screw on it and I don't think
> there's a tab for that on the other one. I might be wrong. Other than
> that I think everything could be swapped, I'd need to exchange throttle
> plate rods I think to get the fittings in place for the throttle cable
> and throttle plate linkage.
I have yet to encounter a multi-carb bike where any two of the carbs are
identical. Not that I have vast experience, just saying that I would be
pretty surprised if it was possible to do this on your XS650 without
some sort of fabrication. It's sort of missing the point, anyway, it
should be possible to inspect each carb and make sure they are 100% clean
without disassembling them from each other.
¿
> It's sort of missing the point, anyway, it
> should be possible to inspect each carb and make sure they are 100% clean
> without disassembling them from each other.
The only way to really be sure that the idle circuit passages are
clean is to squirt
carb cleaner into the pilot air jet and watch it squirt *freely* out
the idle jet and the three acceleration transition ports.
Mark Olson
I totally agree, when I have carbs off to clean them I invariably use
approximately one can of carb cleaner per carb, and I make sure *every*
single passageway and jet, both fuel and air, is 100% clear before
reassembling and reinstalling. I usually visually inspect to make sure
synchronization is approximately right and I always do a vacuum sync
whenever carbs are R&R'ed.
Rob Kleinschmidt
> "Rob Kleinschmidt" <Rkleinsch1216...@aol.com> wrote in message
Even if ring wear on one cylinder would be unusual,
it could be one exhaust valve on it's last legs or very
slightly bent so it's not sealing correctly.
There's definitely a point in troubleshooting
where you stop trying to figure out what's likely
and just start methodically eliminating suspects
one by one.
In this mode, you hit the easy ones first.
Best of luck with it.
Dave
the left carb again, used pretty damn close to a whole can of cleaner, it
was SPRAYING out of the three holes in the throttle body and pilot jet
orifice when squirted through the air jet passage. I also noticed when I
had them off that the carbs seemed to move just a tiny bit in relation to
each other. The machine screws which hold them onto the angle-iron bracket
were wrecked from an over-ambitious philips head driver (rather than an
impact driver) so needed replacement, so I may have eliminated a bit of an
issue there. Put it all back together and...
It idled perfectly on both cylinders. Finally. Good news.
The bad news is that I am WAAAYYYY over-jetted on the mains. Bike ran well
when cold but stumbled up near redline, say 7,500 RPM. So I had an idea I
was a bit oversize. Then started climbing hills, outside and engine temps
warmed up, and 4,500 - 6,000 RPM was unusable, the engine was just choking
on too much gas. The left plug fouled badly and by the time I got home I
was idling on one cylinder again. (Note to self: next time maybe not do the
middle-of-nowhere-through-the-mountains ride as a shakedown ride). I read a
bunch of stuff about the XS650 with BS34 carbs which said one size up on the
mains would improve stock bike. I put on 14" free-flow mufflers (yes, very
loud) and went up two sizes and it was way too much. I think I'll probably
end up back with the original jets, but will try one size up over stock
next.
Next up is front forks... this bike is SCARY on bumpy corners for someone
used to a sport bike with decent handling.
Dave
The Older Gentleman
<snip>
Well done
>
> Next up is front forks... this bike is SCARY on bumpy corners for someone
> used to a sport bike with decent handling.
Oh yes.
--
BMW K1100LT Ducati 750SS Honda CB400F Triumph Street Triple
Suzuki TS250ER Coo, down to just five bikes!
¿
> The bad news is that I am WAAAYYYY over-jetted on the mains. Bike ran well
> when cold but stumbled up near redline, say 7,500 RPM. So I had an idea I
I think I'll probably
> end up back with the original jets, but will try one size up over stock
> next.
Ummmm, what do you think is meant by "one size up over stock"?
Many amateur tuners seem to be under the impression that if they have,
say,
#110 round jets in the stock carbs, going to a #120 round jet is only
one jet size larger.
It's not. It's four sizes larger. The next size larger than #110 is a
#112.5, which passes more than 2.5% more fuel.
The next step above that is a #115 round main jet, etc.
Since the area of a circle = pi times radius squared, the area of the
hole in a 120 main jet is 20% larger and will pass 20% more fuel.
No wonder it drowns the engine at high RPM...
Dave
On Jul 6, 8:14 am, "Dave" <dspear9...@yahoo.com> wrote:
>> The bad news is that I am WAAAYYYY over-jetted on the mains. Bike ran
>> well
>> when cold but stumbled up near redline, say 7,500 RPM. So I had an idea I
> I think I'll probably
>> end up back with the original jets, but will try one size up over stock
>> next.
>
>Ummmm, what do you think is meant by "one size up over stock"?
>
Stock is 132.5. I'm running 137.5, two sizes up from stock like I said.
One size up would be 135, which is what I'll try next.
¿
> Stock is 132.5. I'm running 137.5, two sizes up from stock like I said.
> One size up would be 135, which is what I'll try next.
Well, work out the relative areas of the various sizes, and you'll see
that
the area varies *exponentially*, with the amount of fuel flow
increasing *dramatically* in the sizes above #125.
I have a GS1100 Suzuki bored out to 1168cc and I couldn't use anything
bigger than a #135 in it on the race track.
Dave
On Jul 6, 1:43 pm, "Dave" <dspear9...@yahoo.com> wrote:
>I have a GS1100 Suzuki bored out to 1168cc and I couldn't use anything
>bigger than a #135 in it on the race track.
An 1168cc motor (4-cylinder) would have 4 x 292cc piston displacement. My
650cc twin has 2 x 325cc. So your 292cc displacement piston should draw
commensurately less fuel than my 325cc displacement piston, n'est pas?
Or is this calculation not valid? I'm sure there are other factors than
piston displacement which influence main jet size...
The Older Gentleman
> On Jul 6, 1:43 pm, "Dave" <dspear9...@yahoo.com> wrote:
>
> > Stock is 132.5. I'm running 137.5, two sizes up from stock like I said.
> > One size up would be 135, which is what I'll try next.
>
> Well, work out the relative areas of the various sizes, and you'll see
> that
> the area varies *exponentially*, with the amount of fuel flow
> increasing *dramatically* in the sizes above #125.
>
He knows what he's doing.
¿
> Or is this calculation not valid? I'm sure there are other factors than
> piston displacement which influence main jet size...
A considerable percentage of the fuel burned by your XS650 is actually
used to keep the pistons from melting...
Your calculations are a starting point for comparison, but my GS1100
has four valves per cylinder and peripheral valve area reduces the cam
duration requirement.
The Suzuki 16-valve I-4's use less camshaft duration and they take
about 1/3rd less time to burn the mixture, so less heat is transmitted
to the piston and cylinder head, and the engine requires less fuel.
One of Honda's GP I-4's actually decreased the total burn time to 1/2
that of what their older 16-valve CB750/900/1100's with pentroof
combustion chambers required.
The CB750/900/1100 designs ran hotter than hell...
Dave
"The Older Gentleman" <totallyde...@yahoo.co.uk> wrote in message
news:1j2gdhr.8d2g7f414g5cN%totallyde...@yahoo.co.uk...
Well I don't know as I'd go THAT far, but so far so good. I am no longer
scared of carbeurettors, and will likely pull the carb rack off my CB750 and
clean it next as I've been having problems with that bike too.
Unfortunately as I recall it's a helluva lot more work to get the four carbs
off of the Honda... more friction and less room.
Dave
>
>Your calculations are a starting point for comparison, but my GS1100
>has four valves per cylinder and peripheral valve area reduces the cam
>duration requirement.
>
>The Suzuki 16-valve I-4's use less camshaft duration and they take
>about 1/3rd less time to burn the mixture, so less heat is transmitted
>to the piston and cylinder head, and the engine requires less fuel.
>
>One of Honda's GP I-4's actually decreased the total burn time to 1/2
>that of what their older 16-valve CB750/900/1100's with pentroof
>combustion chambers required.
>
>The CB750/900/1100 designs ran hotter than hell...
I've often wondered what the benefits of multiple valves per cylinder is.
Is it just that it gives a larger orifice to suck fuel through? Is there a
particular benefit to shorter duration cam lifts?
¿
> I've often wondered what the benefits of multiple valves per cylinder is.
> Is it just that it gives a larger orifice to suck fuel through?
Two smaller valves that fit in the same sized combustion chamber have
more peripheral area than one larger valve. The air starts flowing at
lower lift off the seat.
Camshaft designers start figuring the cam duration from when the valve
first lifts 1 mm off the seat until it returns to 1 mm off the seat.
Yamaha tried 4, 5, 7, and even 9 valves per cylinder, before settling
on 5 valves per cylinder on their Genesis motor designed around 1985.
My FZR1000 has 5 valves per cylinder, but Yamaha is giving up on the 5-
valve design because it doesn't deliver power the way they want it to.
If they lower the compression so it will rev, it loses mid-range
power. If they increase compression to get mid range, it won't rev.
4 valves per cylinder seem to be the best compromise. Honda has revved
4-valve engines up to 25,000 RPM.
What the heck? I very seldom use even 8000 RPM. Maybe once or twice in
a long day's ride through the back roads...
> Is there a particular benefit to shorter duration cam lifts?
When the Japanese companies started producing 4 valve per cylinder
engines, the aftermarket cam grinders figured they could just use the
same long durations
on their offerings to the motorcycle hot rodders, but they were wrong.
Their cams didn't work well at lower RPM with the amount of
compression ratio the factories were using.
The new 4-valve engines did better with less duration and a little
more lift...
Most shade tree tuners don't understand what compression ratio does
for them anyway. You need just enough compression ratio to allow your
engine to get over the first hump in the torque curve and through the
mid-range flat spot into the second hump in the curve.
That's where the real power band starts. Too much compression keeps
the engine from taking advantage of the inertia effects of air in the
intake and exhaust systems...
The Older Gentleman
> Unfortunately as I recall it's a helluva lot more work to get the four carbs
> off of the Honda... more friction and less room.
Oh yes. And four hardened carb rubbers as well. Huge fun.
The Older Gentleman
> I've often wondered what the benefits of multiple valves per cylinder is.
> Is it just that it gives a larger orifice to suck fuel through?
Where to start?
OK, greater valve area is the first thing. So more gas in and out,
basically.
With better breathing comes the ability to run leaner mixture and a
higher CR, but there are a lot of variables there. As a rough rule of
thumb, four-valve heads run hotter than two-valve. In times of yore,
some early four-valve heads used to run the risk of cracking round the
valve seats, but that just isn't a problem these days.
Very important: higher revs. Small valves have less reciprocating weight
than big 'uns, so you can run the bike at higher revs before valve float
sets in (that's inertia taking over).
Ignore Krusty's rabbiting on about his ShiteOldSuzuki and old Honda
CB900s - the world has moved on a long, long way in the three decades
since they were built.
>Is there a particular benefit to shorter duration cam lifts?
Depends on the way the rest of the head is built. A longer duration
allows more time to fill and exhaust the cylinder.
However, this sort of breathing tends to work better at high revs than
low to medium revs, when the gas velocity is greater, and decent gas
veocity allows 'scavenging' of the cylinders (outgoing exhaust gas
helping to such in new mixture), which is why you get a situation where
both inlet and exhaust valves are open at the same time... "overlap".
And four-valve heads aid high revs...
There are whole books written on this sort of thing, if you want chapter
& verse.
The Older Gentleman
> Yamaha tried 4, 5, 7, and even 9 valves per cylinder, before settling
> on 5 valves per cylinder on their Genesis motor designed around 1985.
Earlier
>
> My FZR1000 has 5 valves per cylinder, but Yamaha is giving up on the 5-
> valve design because it doesn't deliver power the way they want it to.
And nothing to do with the desire to keep down costs? The 5-valve engine
was/is superb. Even Ferrari used the tech.
¿
wrote:
> And nothing to do with the desire to keep down costs? The 5-valve engine
> was/is superb.
You only need to strip the bodywork off an old Genesis and look at the
mix and
match castings to realize that the thing was designed by feuding
samurai warlords.
After marvelling at the faggots and peas rendered in aluminum, read
the shop manual to realize how difficult one of those would be to
repair if it had starter clutch problems or alternator drive chain
problems.
¿
> Unfortunately as I recall it's a helluva lot more work to get the four carbs
> off of the Honda... more friction and less room.
Mix about 5 ounces of xylene (a paint thinner) with 5 ounces of
acetone, about an ounce of transmission fluid and an ounce of WD40.
Save this mixture in a sealable container, you won't use it all on one
carburetor removal job.
Put some plastic sheeting under the carbs.
Paint the rubber softening mixture onto the rubber boots with a glue
brush and let it work to make the rubber more pliable.
The Older Gentleman
You don'ty get it, do you? The idea of a modern bike (and your old FZR
is anything but) is not to make the thing easy to mend when it brakes,
but to ensure it doesn't break *in the first place*.
Which is what the Japs tend to do.
I'd far rather (say) have a sod of a job replacing (or paying someone to
replace) some obscure component after 40k miles than have to replace
some more easily locatable component every 5k.
The Older Gentleman
Or do what everyone else does, and just soak them in very hot water to
make them pliable.
¿
wrote:
> You don'ty get it, do you? The idea of a modern bike (and your old FZR
> is anything but) is not to make the thing easy to mend when it brakes,
> but to ensure it doesn't break *in the first place*.
And why, pray tell, have the folks at Yamaha re-designed the starter
clutch system to put it on the end of the crankshaft, where it can be
accessed more easily?
Dave
Are there any downsides to using this? I mean, will it shorten the life of
the rubber boots? Not that I'd care... last time I had them off I was about
ready to haul the bike to the scrap yard trying to get those damn carbs back
on.
TOG@Toil
On which FZR1000 have they done this, then?
¿
> Are there any downsides to using this? I mean, will it shorten the life of
> the rubber boots?
Yes, there is an impact on the lifespan of the rubber boots when
solvents that de-vulcanize the rubber are applied.
If the rubber is so hard you cannot remove the carbs, you need to do
*something* to soften them, or you cannot make necessary repairs.
Running a hose from your hot water heater to route very hot water over
the rubber boots is also going to devulcanize the rubber if it's hot
enough.
¿
wrote:
> > And why, pray tell, have the folks at Yamaha re-designed the starter
> > clutch system to put it on the end of the crankshaft, where it can be
> > accessed more easily?
>
> On which FZR1000 have they done this, then?
They haven't done it to the FZR1000, and never will, but they did
redesign the Seca II to move the starter clutch onto the end of the
crankshaft where it belongs.
The folks at Triumph also learned their lesson about burying the
starter clutch and later designs relocated it to the end of the
crankshaft.
TOG@Toil
> On Jul 7, 7:10 am, "Off the Wall" <totallydeadmail...@yahoo.co.uk>
> wrote:
>
> > > And why, pray tell, have the folks at Yamaha re-designed the starter
> > > clutch system to put it on the end of the crankshaft, where it can be
> > > accessed more easily?
>
> > On which FZR1000 have they done this, then?
>
> They haven't done it to the FZR1000, and never will, but they did
> redesign the Seca II to move the starter clutch onto the end of the
> crankshaft where it belongs.
Ae you saying that early Seca IIs had the starter clutch in a
different place?
>
> The folks at Triumph also learned their lesson about burying the
> starter clutch and later designs relocated it to the end of the
> crankshaft.
So what you're actually talking about is completely different designs.
Not modifications of existing designs. It's not really relevant. Some
are different from t'others. And if the component is solid, it doesn't
matter *where* you locate it, really.
And yes, I'm aware that some early Triumphs had starter clutch
problems. So that's a combination of a duff component and awkward
placement. The fact rests: make it reliable to start with and who
cares?
¿
> > They haven't done it to the FZR1000, and never will, but they did
> > redesign the Seca II to move the starter clutch onto the end of the
> > crankshaft where it belongs.
>
> Ae you saying that early Seca IIs had the starter clutch in a
> different place?
Go back and read for comprehension.
> And yes, I'm aware that some early Triumphs had starter clutch
> problems. So that's a combination of a duff component and awkward
> placement. The fact rests: make it reliable to start with and who
> cares?
*I* care, if I'm the one person in a thousand that has to tear my
motor to flinders to replace a component that is supposedly
"reliable".
I'd rather have a less reliable component that is easily accessible
and have the
replacement parts available at Wal*Mart at a bargain price.
The Older Gentleman
> > Ae you saying that early Seca IIs had the starter clutch in a
> > different place?
>
> Go back and read for comprehension.
I have. Because if they redesigned the Seca II midway through its
production run, that's quite interesting.
As we never called Yamahas Secas here it's hard to tell, but the Seca
Two is what we called the Diversion. The previous XJ600 was a *totally*
different bike.
Which rather proves my point.