XS400 carb swap from later model
MisterWhite
out of an old junked xs400 1980 model. Harness seemed in good shape,
engine great, carbs rusted and full of crud from mud wasps. Found a
set from an 82 XS400 Maxim in perfect shape for $20. Modified the
mounting brackets to fit wider mounting (they are closer together on
the 82 head). Figured they would be very similar, found that main jets
were .010 smaller, and pilot jets were bigger. Also, the idle jets do
not have holes in the side of the jet like the older ones. I swapped
all of the old jets to the new carbs, but I still can't seem to get
the thing to idle correctly. With the newer jet setup, it will crank
and run but once it is warmed up you get bad throttle hang when you
let go of the gas (the cable is not binding), and bogging at full
throttle. With the newer jet setup it runs great at full choke but
won't idle. High flow cone filters and straight pipes. Anyone know a
way to get this thing to idle and run without bogging?
MisterWhite
save at full choke. That is using the 1980 jets in the new 1982 carb
bodies. Using the 82 jets in the 82 bodies allows for idle, but bad
bogging at WOT and bad high idle hang at closed throttle.
I am assuming that these carbs are essentially the same bodies save
different jets, floats, bolt ons.
Correct me if that is not the case.
.
> Pardon, on that last part the older (1980) jet setup causes no idle,
> save at full choke. That is using the 1980 jets in the new 1982 carb
> bodies. Using the 82 jets in the 82 bodies allows for idle, but bad
> bogging at WOT and bad high idle hang at closed throttle.
> I am assuming that these carbs are essentially the same bodies save
> different jets, floats, bolt ons.
> Correct me if that is not the case.
Idle RPM hangup when you close the throttle is due to having the idle
mixture screws turned out too far, and *somebody* compensated for
excessively rich idle mixture by turning the idle speed up too far.
This uncovers a pattern of acceleration transition ports that are
controlled by the edge of the butterflies.
This doesn't work worth a damn, the engine bogs on too much gasoline
at very small throttle openings and doesn't clear out until you get
the throttle open more than 1/4 of an inch.
The acceleration transition ports are not supposed to be uncovered
until you barely crack the throttle open as you try to accelerate from
a stop.
The single idle mixture port is rather small on a CV carb, so engine
vacuum can't pull enough mixture through the one hole, so it has to
suck through the other three holes.
Of course you shouldn't be trying to use cross-drilled emulsion type
idle jets in a carburetor that didn't come with them. Emulsion type
jets premix air and gasoline before the idle mixture gets to the idle
circuit.
If you want to look at pictures of all the different jet types, go to
the Factory Pro website and also look at their CV carb tuning guide.
MisterWhite
Thank you so much for the info. I didn't intentionally richen the mix,
the screws were set at 1.5 where they were. I did try to increase the
idle speed, going to play around with it. I am going to put the stock
jets back in, and leave the larger main jets to help compensate for
the pod filters. Another point. The newer carbs did not have the
rubber plugs in the little jet tube, is that normal or simply the
owner forgot to replace them? All the carbs I have dealt with have
them, but I am sure some don't. It also seems to want to idle on one
cylinder, until the mains kick in and then you get both firing. I
think that might be a dying coil/CDI module, possibly unrelated to the
carbs. Again thank you, I really want this to work, the bike turned
out very nice, got my new tires on and covered my seat pan, I want to
ride her!
.
> Thank you so much for the info. I didn't intentionally richen the mix,
> the screws were set at 1.5 where they were.
You can get into trouble swapping idle jets if you don't understand
how the sizing works. You need to understand how the numbering system
for Mikuni and Keihin works.
A #100 main jet has an orifice hole that is 1.00 millimeters in
diameter, so a #125 mainjet has an orifice hole that is 1.25 mm in
diameter.
A #30 idle jet has a hole that is 0.300 mm in diameter and a #42 idle
jet has a hole that is 0.420 mm in diameter. Work out the area = pi X
radius squared formula, and you will see that the area of the #42
pilot jet which you probably have is much larger than the #30 jet's
area.
Carburetors with #30 pilot jets will usually require the idle mixture
screws to be turned out 3.0 to 3.5 turns from lightly seated, but a
carb with a #42 idle jet may need the idle screw to be turned out less
than 1/4 of a turn.
> I am going to put the stock
> jets back in, and leave the larger main jets to help compensate for
> the pod filters.
The 1982 XS400J came with #125 mains and #42.5 idle jets. I can't
imagine you needing anything larger for an engine that small.
> Another point. The newer carbs did not have the
> rubber plugs in the little jet tube, is that normal or simply the
> owner forgot to replace them? All the carbs I have dealt with have
> them, but I am sure some don't.
I don't see any rubber plugs on the parts fiche. Maybe your Yamaha
came with Hitachi carbs, not Mikunis?
It sounds to me like you may be talking about Mikuni BS34SS carbs
which had a
rubber plug in the float bowl concealing the idle jet, and the idle
mixture screws came down from above.
The BS34SS idle jet is supposed to get its fuel through a diagonally
drilled passage
that gets fuel after it passes through the main jet.
A BS30/96 idle jet has ONE cross-drilled hole near the end. You can
look at the Factory Pro website I mentioned previously, or you can
look at Sudco International's website.
> It also seems to want to idle on one
> cylinder, until the mains kick in and then you get both firing.
I suspect that is actually caused by LEAN idle mixture. The single
idle port underneath the idle mixture screw may be plugged up. It's
easy enough to squirt some Berryman B12 or GumOut or STP down that
hole.
CV carbs don't go onto the main jet until the slide lifts all the way
at 7/8ths to full throttle. Until that time, the tapered needle
restricts the fuel flow.
>I
> think that might be a dying coil/CDI module, possibly unrelated to the
> carbs.
That's doubtful. As much as a parts geek at a $tealer$hip might want
to sell you a CDI module or a coil, a CDI usually either works or it
doesn't, and the worst problems with ignition systems nowadays are
just bad connections in the wiring harness.
MisterWhite
Thanks a ton. You really know your stuff. I sort of figured the same
thing about the CDI, either I might have a weak battery or the mix was
wrong. But the battery is new... The 80 XS400 had 135 mains, and the
same idle jet save the crossdrilled holes. The 82 carbs have 125 mains
as you said. The carb bodies APPEAR identical Mikunis #s and all, save
the drain screw is different in the 82 model & it had no rubber plugs,
and has plastic floats.BS34SS 34mm's.
I am going to tear back into them, I assumed I had everything clear
but I will take another look and clean again.
With the pod filters and straight pipes, and assuming that the 80
model originally had 135s, should I use the 125 mains on the carbs, go
with the 135s, or maybe 140s? Thank you again, I am confident I am
close.
.
> Thanks a ton. You really know your stuff. I sort of figured the same
> thing about the CDI
Your Yamaha wouldnot have a real CDI, which means "capacitor discharge
ignition", but ignorant mechanics and parts counter dorks have gotten
into the habit of calling transistor ignition modules "CDI" and we're
stuck with it.
Ignition modules work, or they don't work, there is no in-between
operation where they sort of work occasionally.
The 80 XS400 had 135 mains, and the
> same idle jet save the crossdrilled holes. The 82 carbs have 125 mains
> as you said. The carb bodies APPEAR identical Mikunis #s and all, save
> the drain screw is different in the 82 model & it had no rubber plugs,
> and has plastic floats.BS34SS 34mm's.
> I am going to tear back into them, I assumed I had everything clear
> but I will take another look and clean again.
Getting all the branches of the idle mixture circuit requires spraying
Berryman B12 or GumOut or STP carb cleaner through the idle jet and
the pilot air jet and having a good stream of carb cleaner squirt out
through the single idle mixture port that is controlled by the idle
mixture screw and the three acceleration transistion ports down stream
of the throttle butterfly.
The pilot air jet is sometimes in the carburetor intake, and is
sometimes underneath the rubber vacuum diaphragm.
> With the pod filters and straight pipes, and assuming that the 80
> model originally had 135s, should I use the 125 mains on the carbs, go
> with the 135s, or maybe 140s? Thank you again, I am confident I am
> close.
I can't imagine how an engine that small can use #135 main jets. I
can't use #135's on a GS1100 with pistons that are larger than your
XS400 pistons. I use #125's in my large bore bikes.
Now, if you were running wide-open throttle around Daytona, you'd need
to waste a lot of fuel to keep that air-cooled motor cool but I doubt
that you will ever ride full throttle for more than a mile.
There is a way to tell whether your mixture is marginally lean. When
an engine pings, it deposits little black specks on the nose of the
spark plug that look like pepper. That tells you that you are as lean
as you can safely go on the total jetting.
The next step after pinging is aluminum throw-off. When the total
mixture is seriously lean, the top of the piston starts melting and
you see little silvery aluminum balls on the spark plug.
Tuners used to tell you to look for a light tan color on your spark
plug nose to indicate proper mixture, but that was back in the days of
leaded gasoline.
Nowadays, unleaded gasoline leaves a sooty black ring about 1/16th to
1/8th inch wide deep inside the spark plug where the hot insulator
meets the cooler steel body
and that's why you see race tuners peering down inside the plug with a
magnifying flashlight.
With the advent of 10% ethanol gasoline, an engine that is jetted lean
from the factory will run even leaner, because ethanol carries some of
the oxygen needed to burn it.
If you read the "carburetor tuning guides" that tell you to start
jetting by selecting the main jet that allows the engine to run best
at full throttle, you may get the impression that the main jet and the
idle jet work only at different throttle settings, but this is not
true at all.
The engine sucks more and more fuel through the main jet as you open
the throttle more, but it sucks fuel through the idle jets until the
butterflies are wide open.
It's just that the engine sucks less and less fuel through the idle
jets as you open the throttle more. But that's why I say that you need
to work on your total jetting and get
your idle mixture set for optimum throttle response as you crack the
butterflies open.
MisterWhite
Will do. I will let you know what happens. I am not sure why it has
135s, I thought that was kindof large as well. Possible that someone
put them in there, but it had stock everything and only had 4000 miles
on her when she went down (for 20 years in my cousins barn).
Hopefully, with a little luck, I will be able to run her this spring.
I appreciate all of your information and experience!!! I have a
GS850G, BTW, I love that bike more than any other. Any good way to get
the rear end to stop sliding? Seems like everytime I hit a hard corner
or brake it hard, it wants to come around. Just being shafty I guess.
.
> I appreciate all of your information and experience!!! I have a
> GS850G, BTW, I love that bike more than any other. Any good way to get
> the rear end to stop sliding? Seems like everytime I hit a hard corner
> or brake it hard, it wants to come around. Just being shafty I guess.-
Well, those motorcycles came with hard tires and narrow rims and the
feeling I got in corners was "weak arse", the rear end felt like it
was sinking, no matter what the tire manufacturer was.
A shaft drive might tend to resist the sinking sensation, but the CV
carbs drop their slides suddenly when you roll off the throttle so
that makes the rear end squat a little bit.
A wider rear wheel with a softer tire that fits the wider rim would
help, but the only manufacturer that ever made wider wheels was
probably Lester, back in the early 1980's. If you could find a 3.00-17
or 3.00-18 Lester rear rim and a 2.50-18 Lester front rim you could
make the 850 handle better.
A set of Works Performance shocks would really help rear traction too.
But, why don't you just buy a cheap old sportbike? They came with
wider rims so you can use wider radial tires...
The Older Gentleman
> Thanks a ton. You really know your stuff. I sort of figured the same
> thing about the CDI,
The XS400 was points ignition.
--
BMW K1100LT Ducati 750SS Honda CB400F & SL125
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....
chateau dot murray at idnet dot com
The Older Gentleman
>
> Your Yamaha wouldnot have a real CDI, which means "capacitor discharge
> ignition", but ignorant mechanics and parts counter dorks have gotten
> into the habit of calling transistor ignition modules "CDI" and we're
> stuck with it.
And ignorant dorks don't realise that the XS400 was points ignition.....
The Older Gentleman
> A wider rear wheel with a softer tire that fits the wider rim would
> help, but the only manufacturer that ever made wider wheels was
> probably Lester, back in the early 1980's. If you could find a 3.00-17
> or 3.00-18 Lester rear rim and a 2.50-18 Lester front rim you could
> make the 850 handle better.
For Christ's sake. The GS850G is a shaft drive bike, so rear wheel swaps
are not really an option.
Mark Olson
> For Christ's sake. The GS850G is a shaft drive bike, so rear wheel swaps
> are not really an option.
Depends how determined you are, at least one guy on the Concours Owners
Group forum has had a 17 inch rim welded to the hub of the ZG1000's OEM
16 inch rear wheel. About $450, IIRC.
--
'01 SV650SK1 '99 EX250-F13 '98 ZG1000-A13
OMF #7
The Older Gentleman
> The Older Gentleman wrote:
>
> > For Christ's sake. The GS850G is a shaft drive bike, so rear wheel swaps
> > are not really an option.
>
> Depends how determined you are, at least one guy on the Concours Owners
> Group forum has had a 17 inch rim welded to the hub of the ZG1000's OEM
> 16 inch rear wheel. About $450, IIRC.
Yes, true, and I've seen a few shafty sidecar outfits with interesting
(and expensive) rear wheel mods.
But in this case, my money is on Krusty not realising that we were
talking about a shafty, and weighing in with his usual ignorance.
.
Gentleman) wrote:
> And ignorant dorks don't realise that the XS400 was points ignition.....
Maybe those ignorant dorks are British dorks.
Item #18 IGNITOR UNIT ASS'Y 1 $482.21 Call Us
.
Gentleman) wrote:
> But in this case, my money is on Krusty not realising that we were
> talking about a shafty, and weighing in with his usual ignorance.
What's with this "we" shit? You weren't even in the thread until you
stuck your pointy nose in with disinformation about the XS400 having
ignition points. It didn't.
And Lester made wheels for BMW's, how do you know they didn't make
them for GS850G's?
.
Gentleman) wrote:
> The XS400 was points ignition.
Wrong.
The Older Gentleman
> On Mar 6, 11:03?am, totallydeadmail...@yahoo.co.uk (The Older
http://shop.wemoto.com/pictures.dyn?u=2147869qqq5827940
http://shop.wemoto.com/pictures.dyn?u=2147869qqq5827939
They made two types :-/
The Older Gentleman
> On Mar 6, 11:03?am, totallydeadmail...@yahoo.co.uk (The Older
> Gentleman) wrote:
>
> > The XS400 was points ignition.
>
> Wrong.
http://shop.wemoto.com/pictures.dyn?u=2147869qqq5827940
http://shop.wemoto.com/pictures.dyn?u=2147869qqq5827939
Heh. They made two types :-/
The Older Gentleman
> On Mar 6, 2:07?pm, totallydeadmail...@yahoo.co.uk (The Older
> Gentleman) wrote:
>
>
> > But in this case, my money is on Krusty not realising that we were
> > talking about a shafty, and weighing in with his usual ignorance.
>
> What's with this "we" shit? You weren't even in the thread until you
> stuck your pointy nose in with disinformation about the XS400 having
> ignition points. It didn't.
http://shop.wemoto.com/pictures.dyn?u=2147869qqq5827940
http://shop.wemoto.com/pictures.dyn?u=2147869qqq5827939
They made two types
>
> And Lester made wheels for BMW's, how do you know they didn't make
> them for GS850G's?
BMW rear wheels were interchangeable between many models, so it was a
case of one size fits all. And a lot of BMWs were sold. Also, a lot of
BMWs of the era had spoked wheels, so people were in the market for
alloy wheels. The GS850G had alloy wheels as standard, and Lester didn't
make wheels for them.
End of.
MisterWhite
Gentleman) wrote:
I think the pre 80 xs400 had points, 80-81 had this particular CDI,
and the 82 -> Maxim had another type of electronic ignition.
Thanks for the help though. I love the GS850, 83 GL with 30K, paid
$600, in perfect shape. More fun than a barrel of monkeys, save the
cornering. I think I will check out some shocks, and maybe a softer
tire. The Dunlops on it are a bit rigid and are about half gone
anyway. I put some superbike bars on it, and that really made it a lot
more fun. Next are some new springs, and I will look into shocks. Then
I will get some tires. So many bikes, so little time.
Suzuki GS850
Kawasaki 454LTD
Yamaha XS400
Kawasaki KDX200
Honda CD175
Honda CB750
TOG@Toil
The 850 was a huge heavy lardy thing. We never got the custom version
in the UK, only the pure roadster. I rather liked it, because the
engine was so good. Comfy seat as well. As you say, it didn't corner
too well, but it was a lovely tourer. Good ones are quite sought-after
here.
.
>I love the GS850, 83 GL with 30K, paid
> $600, in perfect shape. More fun than a barrel of monkeys, save the
> cornering. I think I will check out some shocks, and maybe a softer
> tire. The Dunlops on it are a bit rigid and are about half gone
> anyway. I put some superbike bars on it, and that really made it a lot
> more fun. Next are some new springs, and I will look into shocks. Then
> I will get some tires. So many bikes, so little time.
The relatively narrow 16XMT2.75 rear wheel limits you to a bias-ply
tire.
Dunlop recommends their 130/90-16 67H GT-501, but the rear rim is
marginally narrow, probably making the tire "crown" a little in the
center, IOW, you might not be able to lean the motorcycle far enough
without going off the edge.
"L"-model motorcycles have an inherent problem with front-rear tire
mismatches, anyway, the front tire has to struggle to cope with
stabilizing the motorcycle while the 16-inch rear tire is continuously
veering off to the right or left.
A friend of mine tried to race a GS450L that he got cheaply. It scared
him so badly, he quit road racing.
flyrig...@gmail.com
I don't doubt it. The silly 454LTD I have could easily outperform it,
and it is a cruiser. Scary fast at times, however. Not sure how you
can make a bike that is so comfortable yet so fast and agile. I just
wish I liked the way it looked. I feel like a poser biker riding it.
The XS400 I am building should handle fairly well I hope, although it
also has the mismatched tires. It is lowered about 2.5 inches, and
stripped of everything non-essential. Just got the carbs back
together, so tomorrow hopefully I will have good news.
I really love the 850 though. Even with it's problems, I can't help
it. Sounds like a sewing machine (literally), is a bit of a buffalo.
Valve adjustments are a pain, and I used to lose the shifter sometimes
(bent retaining bolt, took me by surprise. Try getting from a dead
stop back into traffic stuck in 5th gear). Really should have come
with a 6 speed. I really wanted a GT750, but this was what I could get
down in south Georgia. On the highway, like you say, at about 70, it
is a smooth riding machine. The only thing I hate about it is
emergency stops. Very unpredictable. If the rear wheel locks, watch
out. You never know where it is going.
I am thinking about an RD400 or a GT550, any suggestions? I can't
afford an H1 or H2. I really want a 2 stroke race bike. I grew up
riding dirt smokers and would love to have a street bike. My KDX200
would be great, except I can't get it tagged. No title or MSO.
The Older Gentleman
> I don't doubt it. The silly 454LTD I have could easily outperform it,
> and it is a cruiser. Scary fast at times, however. Not sure how you
> can make a bike that is so comfortable yet so fast and agile. I just
> wish I liked the way it looked. I feel like a poser biker riding it.
That's a fair assessment. I was actually on the launch of that
horrible-looking thing. It was launched, believe it or not, at Jarama
circuit, Madrid, Spain, alongside the GPZ600R. Present was Kork
Ballington, world 250cc and 350cc champion for Kawasaki.
Korky led the assembled world's press, all mounted on the new 600
sportster, on a couple of sighting laps of the circuit, him mounted on
the 454. Believe it or not, nobody could keep the sod in sight. I have
never ridden with *anyone* like that. It ain't what you've got, it's how
you use it. But's that what being a World Champ is all about, I s'pose.
> The XS400 I am building should handle fairly well I hope, although it
> also has the mismatched tires. It is lowered about 2.5 inches, and
> stripped of everything non-essential. Just got the carbs back
> together, so tomorrow hopefully I will have good news.
They don't handle. They're horrible things, really. And they vibrate
badly. The engine was never fitted with a balancer, and to be honest it
needs it. The engine's quite torquey, but from new they were dogged with
carb problems. I've owned a couple, and the 250. Economical, mind.
>
<snip>
>
> I am thinking about an RD400 or a GT550, any suggestions? I can't
> afford an H1 or H2. I really want a 2 stroke race bike. I grew up
> riding dirt smokers and would love to have a street bike.
RD400 every time. As fast as the 550, lighter, better handling, more
fun, less thirsty. I owned an H1 once. I loved it, but I'd never own
another, except maybe for sunny Sundays.
.
> I am thinking about an RD400 or a GT550, any suggestions?
If I want to get seriously nervous, it's cheaper to chew guarana
berries...
But the ultimate Japanese two strokes are the Yamaha and Suzuki square
fours,
as I recall they were the RV500 and the RG500. I rode both of them and
realized that ownership would require a serious commitment that I was
unwilling to make.
The RD400 Daytona Special was a very nice final version of the air
cooled Yamaha twins that evolved from the earliest copy of a German
design. I had a 1961 YDS1 and a bastard YDS3 that I assembled in 1967
from various parts obtained from $tealer$hips and $alvage yards.
All of those old Yamahas and the R5 and the RD series that evolved
from them were too small for a person of average size. Even the
Daytona Special felt small to me.
And the water-cooled versions like the LC and the RZ350 were still
small and don't seem to be capable of extended high speed operation at
high RPM on open roads, if Bob Nixon's experience proves anything.
I only remember about two riders that had GT550's with the ram air
cooled heads. The GT750 was a much better long distance road machine,
it liked to run at 90 mph all day, and surged and bucked if I tried to
go slower.
I had lots of confidence in the GT750 chassis, after I installed
bronze swing arm bushings and after market shocks and lighter springs
on the back. I used to go squirreling around on mountain roads with
the RD350 guys.
The short wheelbase made the RD350's prone to wheelstanding when they
came on the power and they would also drag their solid footpeg bar
that ran under the engine, so those guys would cobble up their own
footpegs or install aftermarket rearsets.
But the GT750 was always wearing out tires, brake shoes and chains,
and always needed to have the ignition points cleaned and re-set. I
got tired of all the nit-picking maintenance after a few years
> I can't afford an H1 or H2.
Those things are very expensive nowadays.
> I really want a 2 stroke race bike. I grew up
> riding dirt smokers and would love to have a street bike.
Well, if you don't have to ride very far, and you do most of your
riding on back roads,
an RD400 will probably work just fine.
There are also grey market 2-strokes like Aprilias with Suzuki 250
motors and Honda triples. I think the triples were NS250's.
If you can find somebody who have gotten an Aprilia registered for the
street in any state, it might be worth considering, even if it does
cost $5K.
Some local riders bought the grey market two strokes to ride on the
Angeles Crest Hwy above Pasadena. The 2-strokes are so thirsty, they
can barely make it 25 miles up to the roadhouse at Newcombs Ranch,
then they have to go back down the hill to buy gasoline.
But the short wheelbase 2-strokes don't need to lean so far over to go
through a turn, so they can go around the curves very easily.
MisterWhite
Gentleman) wrote:
I finally got the guy running, wow. I was running WAY too rich, ended
up with 1/2 turn out on the idle screw. I assumed I would be running
rich with the pods and straight pipes, but the different carbs must
have changed things. Turns out these idle jets don't have the plugs,
they pull fuel directly from the bowl. So I ended up with the 82 pilot
and idle, and the 135 main from the 80 carbs. The bike has WAY more go
that stop I am afraid, the single disc in front and wimpy drum in back
don't want to slow the guy down. It accelerates like a monster, and
sounds fantastic. My neighbors probably hate me now. I am removing the
starter tomorrow, anything special need to do to take it out? Adjust
the valves next, still need to balance the wheels. It doesn't exactly
handle great, but it is fun to drive. I was hoping for a better
tracker, but it probably won't do the job. Oh well, fun build anyway.
Maybe the CB750 SOHC?
The Older Gentleman
> And the water-cooled versions like the LC and the RZ350 were still
> small and don't seem to be capable of extended high speed operation at
> high RPM on open roads, if Bob Nixon's experience proves anything.
Wrong. One even competed in the Bol 'Or 24-hour race (and finished!).
paul c
A guy from Britain told me that the RD350's caused a change in the UK
graduated licensing laws because because newly-licensed teenagers could
immediately outdrag most cars if they had one of those bikes.
Apparently before they came out, the authorities equated displacement
with speed. Is this true?
I got a kick out of taking apart an old Suzuki (IIRC) 500cc engine that
had two crankshafts. You could see how it was actually two of their
250cc two-stoke engines put together. Maybe somebody here can remember
the model (I think the nickname for the smaller one was Gamma) but
apparently both are quite prized now.
The Older Gentleman
> A guy from Britain told me that the RD350's caused a change in the UK
> graduated licensing laws because because newly-licensed teenagers could
> immediately outdrag most cars if they had one of those bikes.
> Apparently before they came out, the authorities equated displacement
> with speed. Is this true?
No. It's complete nonsense.
They did a 250cc version of the RD, and at the time there was a 250cc
learner limit. A year or two later they dropped the learner limit to
125cc, but that was because when the 250cc limit came in, years before,
a decent Brit 250 was pushed to exceed 70mph, whereas the Japanese were
building 90-100mph 250s from the early 1970s.
It's debatable whether the RD250LC contributed to the 250 learner ban.
It certainly didn't help.
>
> I got a kick out of taking apart an old Suzuki (IIRC) 500cc engine that
> had two crankshafts. You could see how it was actually two of their
> 250cc two-stoke engines put together. Maybe somebody here can remember
> the model (I think the nickname for the smaller one was Gamma) but
> apparently both are quite prized now.
RG500. They did a 400cc model too. The Yamaha RD500 also had two cranks.
Yes, they're hugely collectable.
MisterWhite
Gentleman) wrote:
Have been having fun riding it, still have a bit of a backfire in the
right side cylinder (farthest from inlet).
The left side has no backfire. Both are a nice blue in the colortune,
save the backfires bright white. Any ideas?
.
> Have been having fun riding it, still have a bit of a backfire in the
> right side cylinder (farthest from inlet).
> The left side has no backfire. �Both are a nice blue in the colortune,
> save the backfires bright white. Any ideas?- Hide quoted text -
It might be lean idle mixture on the right hand side, so open the idle
mixture screw another 1/4 of a turn to see if that helps. If the idle
mixture port is dirty, it may clean out, and then the idle mixture
will be too rich again.
I add about 4 or 5 ounces of Berryman B12 to a full (5 gallon) tank of
gas a few times a year to keep the idle mixture ports clean.
Another possibility is that your intake valves have a build up of
carburized oil on the valve heads which keeps them from seating.
If your engine smokes on one cylinder when you start it, it may be oil
leaking past the valve guide oil seals, down the valve stems. Chevron
makes Techron Concentrate to clean off the intake valves.
MisterWhite
If there is carbon on the valve seats, would that require a valve job
to fix, or could I just knock it off? I am going to readjust them
tomorrow when they are cold, i will inspect them. I call myself
cleaning the carbs thoroughly, but I will re-examine. Thanks everyone!
This bike handles surpisingly well for a home build. I am still a bit
nervous about taking too hard of a lean on it, not knowing how it will
react to the harder shocks and the lower stance, but I am getting
there.
.
> If there is carbon on the valve seats, would that require a valve job
> to fix, or could I just knock it off?
You can decarbonize an engine by CAUTIOUSLY spraying a fine mist of
water into the carburetor intakes while revving the engine up.
The carbon will come flying out the exhaust pipes.
But, don't go crazy with the water spray. You could bend a rod if you
hydraulically lock a cylinder at high RPM...
There are also chemical fuel additives that you put into the gasoline
to decarbonize a cylinder. If the chemical contains a lot of alcohol,
you need to be careful with high RPM, as alcohol tends to wash the oil
film off the cylinder walls...
MisterWhite
Thanks for the info. It seems to clear up when warmed up, so I am
thinking it is carbon.
Now I have another problem. Once the bike warms up good, and starts
running well, if I bring it to a sudden stop, it shuts off almost like
the switch was flipped. I can then not get it to crank back up for a
while. It almost seems like it is running out of gas, but priming the
engine doesn't help. Overheaded CDI? Coil? ANy ideas? I am removing
the starter tonight (can't use it anyway, it pulls so much juice from
the ignition it won't fire!) and some other stuff, so any ideas would
be appreciated while I have it apart. Thank you guys for all of your
help, if you are ever in south Georgia holler and we'll go for a ride.
.
> Now I have another problem. Once the bike warms up good, and starts
> running well, if I bring it to a sudden stop, it shuts off almost like
> the switch was flipped. I can then not get it to crank back up for a
> while.
You might have tight valve clearances that prevent the engine from
making enough compression to start. Carbon on the valve heads will
cause the valves to tighten up.
> It almost seems like it is running out of gas, but priming the
> engine doesn't help.
It might be vapor lock. Cautiously open the float bowl drain and see
if gasoline runs out. Don't get gasoline on your hot exhaust pipe
though.
Don't ask how I know that.
Overheaded CDI? Coil? ANy ideas?
When an ignition coil overheats the engine starts shooting ducks out
the exhaust pipe. Boom. Boom.
Your motorcycle doesn't have a true CDI, it has a transistorized
ignition module. They usually either work or don't work,
and the only times I ever had a module that acted weak was the ones
inside the distributor of my car.
Those modules were exposed to engine heat and steam from overheated
engines.
I went down to Pep Boys and asked for the ignition gizmo that went
inside my distributor, and the guy came back with an ignition lock.
I said, "No, I need the little circuit board that goes *inside* the
distributor."
He sez, "We don't have nothin' like that."
His more experienced co-worker said, "He needs the ignition modjoe."
I said, "Yeah, that's it. I need the modjoe."
So I installed the new modjoe and it worked for another 100,000 miles.
MisterWhite
Wow, sounds like some of the parts places around here...
I had a modjoe ;-) on my 86 Pontiac Fiero (or Fierjoe) that died every
1000 miles or so... It had a lifetime warranty so I swapped it like
100 times. The guy said "we can't keep doing this if you are
overheating the module" I said "your part claims it is an OEM
replacement, and this is the (albeit badly designed) OEM engine, and
it makes a lot of OEM heat. If it can't take it that ain't my
problem". He saw it my way until I lost my reciept... Funny thing was,
the original one worked fine forever until I changed distributors and
forgot to take it off of the core. I then bought a true ACDelco module
and it burned up too. Never did figure that one out.
I will try opening the bowls, I thought of trying that too. I hope you
weren't too badly burned learning that lesson ;-)
If it is vapor lock, could it be that my tank is not breathing?
.
> I will try opening the bowls, I thought of trying that too. I hope you
> weren't too badly burned learning that lesson ;-)
No, fortunately there wasn't much gasoline left in the fuel hose. I
just got a flash of flame and it was done.
What happened was I'd bought a brand new Yamaha engine from a $tealer
$hip for a good price, as somebody had ordered the engine and then
decided they didn't want it after all. The $tealer$hip probably made
money off of me and guy who'd paid for it.
The first time I rode the motorcycle it started overheating and I
noticed that the idle was too fast. I momentarily thumbed the kill
button and the engine didn't slow down, because it was actually being
ignited by the overheated spark plugs.
It was really idling too high, so I turned off the gas. Then I
disconnected both spark plugs. I pulled the fuel hose off and got the
little fire I described.
I was removing the spark plugs when the engine finally stopped
running...
> What If it is vapor lock, could it be that my tank is not breathing?
It's easy enough to remove the gas cap and see if that helps get the
engine started sooner.
Riders used to install clear plastic fuel hoses so they could see if
there was any gas in the lines. They would *always* see
air spaces in any bend in the line.
No matter how they re-routed the lines, they could never get rid of
the bubbles. Air spaces in the gas lines can get so hot that the
evaporating gasoline creates a pressure in excess of the static
pressure head due to the weight of the gasoline in the tank.
There is only about 0.25 psi of static head on the gasoline in the
line. At least you cannot see air bubbles in the black rubber fuel
hose that is standard equipment of motorcycles.
I ran into a problem using *automotive* fuel hose which is thicker and
has a fabric cord between layers of rubber.
I bought a set of carburetors from a friend, and he'd been using the
automotive hose.
I didn't realize that the hose was so thick it was kinking up under
the gas tank and was shutting off the flow of gasoline.
I was stuck on the highway and couldn't get home without climbing a
hill. The motorcycle would quit everytime I went uphill.
I theorized that the fuel line must be kinking, so I removed the rear
bolts from the gas tank and stuck a crushed beer can under the tank to
prop it up, and then I could ride up the hill and get home...
All the crap I went through learning how to keep a motorcycle running
makes me realize how many silly things can keep a bike from running.
MisterWhite
Any thoughts on converting this to kick only? I have removed the
starter, and will make a nice bracket to replace it so I can bolt the
cover back over the hole.
Only thing I seem to have trouble with is the battery. I have tried
removing it and going with a huge capacitor, but i can't seem to get
it to crank without a battery charger. Once it gets going it is fine,
but getting it going is not easy. Any ideas? Headlight also won't come
on, I have replaced the diode to the relay, I guess it was a 12V
zener??? No info on that guy anywhere...
The Older Gentleman
> Any thoughts on converting this to kick only? I have removed the
> starter, and will make a nice bracket to replace it so I can bolt the
> cover back over the hole.
> Only thing I seem to have trouble with is the battery. I have tried
> removing it and going with a huge capacitor, but i can't seem to get
> it to crank without a battery charger. Once it gets going it is fine,
> but getting it going is not easy. Any ideas? Headlight also won't come
> on, I have replaced the diode to the relay, I guess it was a 12V
> zener??? No info on that guy anywhere...
It's a pretty crap bike with carbs that were notorious for problems, and
an electric starter that didn't spin the engine fast enough.
You can't polish a turd.
--
BMW K1100LT Ducati 750SS Honda CB400F, SL125 & SH50
MisterWhite
Gentleman) wrote:
Thanks for your creative input. It is actually very fast for what it
is. Needs a rear disc though, the drum won't really stop it well.
I don't want the starter, that is my point. I have removed it. I just
want it to crank without a battery. But thanks anyway.
MisterWhite
Gentleman) wrote:
Oh and it was free. I have other bikes, this one is just for fun, and
helpde me learn some new painting, fabrication, and welding
techniques.
The Older Gentleman
> Thanks for your creative input. It is actually very fast for what it
> is.
Nonsense. Torquey, but not fast. Definitely not fast. And *certainly*
not "very fast for what it is", which is a meaningless phrase anyway.
Fast for a 400 twin? No. Fast for a cruiser? No. Fast for a 1970s
design? No.
>Needs a rear disc though, the drum won't really stop it well.
Not really. The drum is fine. You should be doing most of the braking on
the front brake anyway. If the drum isn't up to snuff, strip it, clean
it, fit new shoes.
> I don't want the starter, that is my point. I have removed it. I just
> want it to crank without a battery. But thanks anyway.
Like I said, the damn things were hard to start when new. The problem is
the carbs. You can convert them to kick, sure - early XS400s had a
kickstarter. But they were always less-than-mediocre bikes.
As a free bike, it has its merits. And the engine was always tough and
reliable. But they were still pretty poor bikes. I've owned two. Oddly,
I have a soft spot for them, but then I like all types of crap bikes.
--
BMW K1100LT Ducati 750SS Honda CB400F, SL125 & SH50
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....
MisterWhite
Gentleman) wrote:
It IS an XS400. It IS much faster than it WAS. Hence fast for what it
IS. An XS400. I am not a huge Yamaha fan anyway, and I don't think it
is a great bike. I am trying to make it a better bike, for fun you
know? Thanks anyway for all your help dude, try to have some fun.
.
> Any thoughts on converting this to kick only? I have removed the
> starter, and will make a nice bracket to replace it so I can bolt the
> cover back over the hole.
> Only thing I seem to have trouble with is the battery. I have tried
> removing it and going with a huge capacitor, but i can't seem to get
> it to crank without a battery charger. Once it gets going it is fine,
> but getting it going is not easy. Any ideas? Headlight also won't come
> on, I have replaced the diode to the relay, I guess it was a 12V
> zener??? No info on that guy anywhere...- Hide quoted text -
If you have a re-chargable 12 volt battery to power the transistor
ignition unit, it will probably
keep the engine running until voltage drops below ~11 volts.
The problem with a permanent magnet alternator with shunt type
rectifier regulator is that it still needs
a rechargable battery of some reasonable ampere hour capacity to
provide system stability.
The six diodes in the rectifier are getting up to 120 volts from the
generator, but the battery is pushing back the other way, and the
battery's substantial power keeps the alternator's output voltage down
to only about 20 volts maximum.
The voltage regulating circuit inside the rectifier regulator is a
small zener diode that triggers the gate of a silicon control
rectifier. When triggered, the SCR shorts one phase of the alternator
to ground, and that reduces the alternator power by half.
The SCR has enough internal resistance, so it's not a dead short to
ground and it survives shunting alternator power to ground many times
per minute at high RPM.
The earliest permanent magnet alternator designs were unregulated
beyond using the headlight, tail light, and instrument lights to burn
up excess "juice" from the alternator at higher RPM. You could run
those motorcycles with the battery removed from the system, but, if
the head light burned out, the tail light and all the other bulbs
would burn out too.
Suzuki added a tiny little diode to some models, it may be have been a
zener, and the British bikes had that great big zener mounted under
the headlight. It did what the zener and SCR in a modern rectifier
regulator did.
The old Brit bikes (and little Japanese singles) had what was called
an "energy transfer magneto". The alternator produced a rather low
voltage which was fed to the ignition coils and the ignition coils
tranformed the low voltage to high voltage.
But these motorcycles all had ignition points and a points type
ignition will start off of a rather low voltage, while the
transistorized ignition needs that steady ~11 volts or so.
It may be possible to convert your bike to ignition points in order to
get rid of the battery *and the transistorized ignition box*, but
there are still problems.
The state I live in used to require any motorcycle to at least have a
battery that was capable of lighting the tail light only for half an
hour, but some of my battery-hating friends bought Battery Eliminators
which were just a huge capacitor (or a bank of capacitors).
I don't know what the value of the capacitors was, but without a
battery to resist the excess voltage from the permanent magnet
alternator, your transistor ignition box is going to get hit with some
wildly-varying voltages.
The Older Gentleman
> It IS an XS400. It IS much faster than it WAS.
Not what you said originally.
> Hence fast for what it
> IS. An XS400.
Not what you said originally.
>I am not a huge Yamaha fan anyway, and I don't think it
> is a great bike. I am trying to make it a better bike, for fun you
> know?
Fair enough. OK: in practical terms, there's not much you can do with
the engine. Nobody made tune-up kits for them AFAIK. And they were not
the most powerful 400s anyway. They have one asset, which is the nice
wide torque spread: far better than the other 400 twins of the era, with
the possible exception of the Kawasaki 400/440cc twins.
So leave the engine alone, and sort out the carbs as best you can. These
are the notorious weak spot of the bike. Absolutely everything needs to
be spot on.
Handling: you can improve the front end feel by jettisoning the rubber
mounts on the handlebars (if that hasn't been done already). You'll get
more vibes through ther bars, but I'd experiment with bar end weights if
it irritates you.
However, ideally you want to throw away the OE cowhorns and fit much
flatter lower bars. The OE bars make the front end too light.
Back end: decent shocks will help, and also decent rubber. There's not
much you can do about the huge heavy 16" rear wheel.
MisterWhite
Gentleman) wrote:
Thank you. I think that is pretty much what I am doing. Doesn't seem
to be a lot you can do with the engine, and that isn't a big deal to
me. It is fast enough for what I want it for. I think the stock motor
claimed 14 seconds in 1/4 mile, that is OK. I tossed the crazy bars,
and have some clubman bars on it (ebay junk). I wanted clip ons but
man they are higher than a cat's back. I got a nice pair of lowered
shocks from a guy on ebay, really stiff. I have some XS360 fork
cushions, about 1.5" lower than the XS400 (although I can't seem to
find out how much oil they take, anyone?) And they are very stiff. The
lowered center of gravity make the bike feel better and more stable,
al least to me. I will mill some aluminum bushings to replace the
rubber ones when I can get back to the machine shop, see how that
does. I saw an XS400 rear wheel on ebay with a disc, it "said" it was
18". I don't think that is correct, anyone verify that? Looked like
the same wheel as mine, but with disc. I thought they were all 16" on
the rear? I think I have it running pretty well, once it warms up the
popping stops and the plugs have a nice tan appeal when they come out.
Only problem now is I can't seem to get any damned voltage to the
headlight, even with the bike running. Going to test the relay and see
if it is bad.
I appreciate all of the help, have a nice one. Beautiful riding
weather where I am right now. Hope the same is true for everyone else!
TOG@Toil
That's about right.
<snip>
I saw an XS400 rear wheel on ebay with a disc, it "said" it was
> 18". I don't think that is correct, anyone verify that? Looked like
> the same wheel as mine, but with disc. I thought they were all 16" on
> the rear?
No, the roadster (ie: not cruiser) version had an 18" rear wheel and a
single disc brake at each end.
JS
wrote:
>
> - Show quoted text -
I also see there is a 16" disc version, I might try and swap it over.
I have the MC and caliper already for the rear...
I am still having the "runs but won't crank back up after it is hot"
problem. I have decided it must be a constant open in a circuit
somewhere that can't make once it heats up. It can bridge the air gap
while running, but not after it is shut off. Possible the plugs or
proximity sensor or coils? Anyone know which is more likely? I am
goign to try new plugs today, and the coils maybe next. I can't seem
to figure out a way to get to the sensor, the cover doesn't wat to
come off of the locator pin. The screw on the left side comes out, but
how do you get the right side loose? 1980 XS400.
The Older Gentleman
> I also see there is a 16" disc version,
Ah, we never got that oen in the UK.
> I might try and swap it over.
> I have the MC and caliper already for the rear...
> I am still having the "runs but won't crank back up after it is hot"
> problem. I have decided it must be a constant open in a circuit
> somewhere that can't make once it heats up. It can bridge the air gap
> while running, but not after it is shut off. Possible the plugs or
> proximity sensor or coils? Anyone know which is more likely? I am
> goign to try new plugs today, and the coils maybe next. I can't seem
> to figure out a way to get to the sensor, the cover doesn't wat to
> come off of the locator pin. The screw on the left side comes out, but
> how do you get the right side loose? 1980 XS400.
IIRC you want to pull it off the bottom locator, and then lift it
slightly. I think there are L-shaped lugs that hold the top edge in
place, but ICBW.
JS
Gentleman) wrote:
Thanks for the info. Tried swapping the plugs, that seemed to helped
it start and idle a bit better, but it didn't fix it. Now it acts like
it is running out of gas, and eventually dies and will not crank up.
There is gas, and gas in the bowls. No vapor lock in the tank. Next
time I will pull off the tank and check the coils for voltage while I
kick it over, if they aren't getting anything from the sensor I guess
I know that is it, if they are then I guess that means the coils.
Might be overlooking something. It is fun to ride while it lasts, as
you say very torquey. (sp?) Sounds good too, almost like a real
bike ;-)
Have a good one, and thank you.
JS
>
> - Show quoted text -
I think I have isolated the problem to defective plug wires. I tested
the resistance in both coils, wires, and connectors, and found one
wire 3 times the resistance of the other, and the other wire's
connector appear to open intermitantly. After replacing the wires with
some auto ignition wires i had lying around, the bike started right
up.
I never suspected the end would be bad, but now that I think about it
the bike was dropped on the right side, and that is the side with the
bad plug end (duh!). Thanks everyone.
Wudsracer
***************************************
>On Sat, 15 Mar 2008 21:04:37 +0000, totallyde...@yahoo.co.uk (The Older Gentleman) wrote:
>
>You can't polish a turd.
*******************************************
That reminds me of a quote from Dirtcrasher:
"You can't polish a turd, but if you drink a quart of olive oil, it
will come out nice and shiney."
Sorry for the interruption.
Wudsracer/Jim Cook
Smackover Racing
'06 Gas Gas DE300
'82 Husqvarna XC250
Team LAGNAF
The Older Gentleman
> hat reminds me of a quote from Dirtcrasher:
>
> "You can't polish a turd, but if you drink a quart of olive oil, it
> will come out nice and shiney."
>
> Sorry for the interruption.
No apologies needed. I rather like that.
--
BMW K1100LT Ducati 750SS Honda CB400F, SL125 & SH50
chateau dot murray at idnet dot com
"What you're proposing to do will involve a lot of time
and hassle for no tangible benefit."