'81 Maxim 650 - Popping, backfiring with gas + carb cleaner
donote...@ekkinc.com
I imagine this is somewhat common, however I'm a new rider and I'm
worried I've done some harm to my 1981 Yamaha Maxim 650.
Background, with all my mishaps included:
When I bought the bike a couple of weeks ago, it appeared to run great
- started up every time, accelerated smoothly, no apparent issues.
Then, I went out of town and didn't ride the bike for 6 days. I don't
know how old the gas was that was in the tank - I'm assuming it was a
couple of weeks old. Well, I left the petcock in the PRI position,
not realizing that I have a different type of petcock than the bikes
we trained on in the MSF class and I now know that the PRI position
lets gas flow freely into the engine, which can cause big problems in
rare circumstances but I'm sure is always a bad idea when you have old
gas in the tank. When I tried to start it up the first time after my
trip out of town, it wouldn't start. I tried for 10-15 minutes to get
it going, but I then gave up. I returned two days later after doing a
little research, sprayed a little bit of starter fluid into the air
box, and the bike started up. I had to rev the engine a bit to keep
it running, it would die if I let it idle with or without the
choke. So, once I was confident that the bike would start, I
drained the gas out of the tank, filled it up with fresh gas, and put
about 4 ounces of B12 Chemtool Carb Cleaner in the tank. I then
switched the petcock to 'On' (at this point I still didn't know what
PRI meant), put a shot of starter fluid into the airbox, started it up
and once it was warmed up it would idle fine. I then went for a ride
around town, which consisted of mostly under-35 mph riding, just to
get the carb cleaner working. It ran great for the first 45 minutes
of the ride, but then suddenly performance went way down. It started
stalling at stop lights unless I revved the engine, and usually when
first accelerating from a stop it would not accelerate smoothly at
all. There were frequent pops and the occasional backfire coming from
the exhaust, and I was putt-putting along with the throttle cranked up
pretty high. After about 50 feet of this putt-putting, something
would catch, the RPMs would jump up to over 3K and it would start
accelerating quickly. So, I put up with this the rest of the way
home, which was about a 10 minute ride, and I then parked the bike and
put the petcock back to the PRI position. The next day I read that
PRI means prime, and it's bad to leave it in that position, so I set
it to ON later that day, as soon as I could. After a few hours, I
tried starting it up again to see if it would idle, but it wouldn't, I
had to rev the engine to keep it running and there were still frequent
pops and the occasional backfire.
One other thing - I have receipts for quite a bit of work that the
previous owner had done just a little over a year ago, including carb
overhauling and new spark plugs.
Are the symptoms I'm describing just indicating that the carb cleaner
is doing what it needs to do or have I done some damage with my
mistakes? I haven't checked if the plugs have been fouled, I plan to
check that this weekend.
I'm comfortable doing routine maintenance on my cars (fluid changes,
spark plugs, brakes), so I think I can handle maintenance on the
motorcycle, however big jobs like carb synchronization scares me. I
have a manufacturer's maintenance manual for this bike.
Thanks in advance for any assistance.
Ken
Albrecht via MotorcycleKB.com
>Are the symptoms I'm describing just indicating that the carb cleaner
>is doing what it needs to do or have I done some damage with my
>mistakes? I haven't checked if the plugs have been fouled, I plan to
>check that this weekend.
Sounds normal to me. I can just imagine how filthy your carbs are inside.
Doing the B12 in the gas tank trick is sort of like taking a laxative when
you're really constipated.
It's going to come out suddenly. But some of it may not want to come out at
all...
That's when you need an enema. B12 also makes aerosol carb cleaner in a
pressure can for that
stubborn crud in your carbs.
If your carbs have a lot of crud in the float bowls, the B-12 will loosen it
and it will go through all the
ports and passages causing a lean mixture and you will hear the exhaust pipes
of inline-4's making "piffle-piffle-SNAP" sounds as you roll off the throttle
to slow down.
Large bore engines, like v-twins will make a fart-BANG! when you roll off the
gas, suddenly making the idle mixture very lean.
The B12 will dissolve all the gum and varnish, and it's possible that the
crud from your gas tank
kept the float valves from closing properly, so the level in the float bowls
was too high and the engine was running way too rich.
Or, maybe you were riding with the choke valves open a tiny bit to keep the
engine running.
Your carbs don't have a real choke plate, they have a bypass valve that sucks
gasoline right out of the float bowls. When an engine with dirty carbs warms
up and you're trying to ride with the choke valves open, the idle RPM will be
way too high.
>
>I'm comfortable doing routine maintenance on my cars (fluid changes,
>spark plugs, brakes), so I think I can handle maintenance on the
>motorcycle, however big jobs like carb synchronization scares me.
Carb $ynchronization is a big money maker for the $tealer$hip$. A newbie
comes in with an engine that is running a little rough because the bike has
been in storage all winter, and the mechanic$ are only too happy to offer to
$ynchronize the dirty carbs.
Then, when the rider goes out for his spring ride and the alcohol additves in
his fresh gasoline start working on the carbs, the jets and passages get
cleaned out, but the engine *still* runs rough because of the unnecessary
$ynchronization that has changed the relative positions of the throttle
butterflies...
--
Message posted via MotorcycleKB.com
http://www.motorcyclekb.com/Uwe/Forums.aspx/tech/200705/1
mk10
> Are the symptoms I'm describing just indicating that the carb cleaner
> is doing what it needs to do or have I done some damage with my
> mistakes?
No, you didn't do anything that would totally screw things up--things were
already screwed up. You may have thought that everything was OK, before you
worked on it, but you were wrong--things were not OK. As another poster
pointed out: gunk, dirt, varnish, and your choke circuit were all
compensating and making you think that everything was normal.
> I'm comfortable doing routine maintenance on my cars (fluid changes,
> spark plugs, brakes), so I think I can handle maintenance on the
> motorcycle, however big jobs like carb synchronization scares me. I
> have a manufacturer's maintenance manual for this bike.
If it were me I'd clean the carbs the proper way, not the "spray some stuff
down into the carb throats" cheat method. You'll need to pull the carbs off
the bike and take them apart if you really want to get them clean. All it
takes is one small piece of crap in just the right spot inside to make the
bike run rough. And, after you do this disassembly/reassembly job, you won't
think that synchronizing carbs is such a big deal anymore.
chateau...@btinternet.com
> Hello,
>
> I imagine this is somewhat common, however I'm a new rider and I'm
> worried I've done some harm to my 1981 Yamaha Maxim 650.
>
> Background, with all my mishaps included:
> When I bought the bike a couple of weeks ago, it appeared to run great
> - started up every time, accelerated smoothly, no apparent issues.
> Then, I went out of town and didn't ride the bike for 6 days. I don't
> know how old the gas was that was in the tank - I'm assuming it was a
First thing is to determine how well it ran originally, and for how
long.
Easy starting? Smooth idle? Free revving? OK to redline? Running fine
for a couple of hours? Had the bike been in regular use before you got
it? If the answers to all these questions are yes, then it's not
gummed carbs.
It all sounds like carb trouble, but if the bike was running fine
before, then the carbs won't magically have gummed up in just six
days. No way. Could be a coil starting to go, for instance: I've had
that happen twice on old Jap bikes, and the first time it fooled me
into thinking it was a fuel problem, because the symptoms were so
similar.
What makes you think the fuel was only a couple of weeks old? If it
was, and the bike had been in regular trouble-free use, then it's not
gummed carbs.
If it had been laid up for some years immediately before you got it,
and you only ride it for five minutes then maybe it is gummed carbs,
or quite possibly crap from the tank in the carbs (though I'd have
thought the fuel filter in the tap would catch it)..... And you've
been given two reasonable answers as to what to do next.
donote...@ekkinc.com
It's true there's a lot I don't know about how this bike was treated
in recent years. I do know that the guy I bought it from quit riding
because his knees went out on him. Jan 06 he put about $1000 worth of
work into the bike - including carb reconditioning, tune up, battery,
new fork seals, front brakes, new float bowl gaskets, new air
filter. In April he got the carb needles replaced. I believe he
rode it at least part of last season after that. I'm checking with
the seller now to see what more he can tell me.
I want to burn at least through this tank of gas with the carb cleaner
in it, then if it isn't any better I'll look into the suggestions that
have been made. Problem is, the engine consistently stalls when
idling, and then it won't restart without some starter fluid. I'm
thinking I don't want to ride around with starter fluid strapped to my
bike, so since I've started having trouble I've only ridden the bike
around the neighborhood. It's become quite a pain to go through this
tank of gas. Is there anything I can do to keep the bike from
stalling other than holding on the throttle whenever it's supposed to
be idling?
I think
ott...@hotmail.com
Why not just drain the Gas out of the tank, either thru the petcock,
or take the tank off and empty it? Does sound like it might be Coil
though?
Bg
Albrecht via MotorcycleKB.com
>I want to burn at least through this tank of gas with the carb cleaner
>in it, then if it isn't any better I'll look into the suggestions that
>have been made. Problem is, the engine consistently stalls when
>idling, and then it won't restart without some starter fluid. I'm
>thinking I don't want to ride around with starter fluid strapped to my
>bike, so since I've started having trouble I've only ridden the bike
>around the neighborhood. It's become quite a pain to go through this
>tank of gas. Is there anything I can do to keep the bike from
>stalling other than holding on the throttle whenever it's supposed to
>be idling?
Look for the master idle knob or screw on the carburetors. It adjusts all
four throttle butterflies at once,
you don't want to adjust one butterfly at a time and unsynchronize the carbs.
On Mikuni and Keihin carbs, the master idle knob is betwwen the #3 and #4
carbs (the ones on the right hand side of the engine as you sit on the bike).
You can turn the knob up for now, and when the carbs are cleaned out, you can
turn it back down.
http://www.bikebandit.com/partsbandit/showschematic.asp?dept_id=650201
Yamaha used Hitachi carbs that are similar. Item #49 is probably related to
the master idle control.
Item #46 is the EPA anti tamper plug that keeps owners from adjusting the
idle mixture screw (#44).
If you look down on the top of the carbs and see the slotted head of the idle
mixture screw, somebody has drilled out the EPA plug.
It's easy enough to drill the plug out yourself. You drill a small starter
hole, then make it a little larger and screw a small sheetmetal screw into
the hole and pull out the screw and plug with a pair of pliers.
Then you can screw the idle mixture screws all the way clockwise until they
just stop turning. Count the number of full turns and fractions of turns and
write the number down.
Do that for each screw, then remove it, making sure you get the small spring,
washer and o-ring out of the hole. Keep each screw separate from the others.
Then you can squirt aerosol carb cleaner down the hole that the screw came
out of and reinstall the screws. Turn them all the way clockwise, then back
them off to the same number you wrote down for each screw and you're back to
the original factory setting.
An extra 1/8th or 1/4th of a turn out from factory setting will help the
engine start easier, warm up faster, and'accelerate better.
--
Message posted via http://www.motorcyclekb.com
The Older Gentleman
> I believe your bike has a pionts and condensor ignition.
Wrong.
--
BMW K1100LT 750SS CB400F CD250 SL125
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....
donote...@ekkinc.com
wrote:
I'm still having some trouble getting my Maxim 650 to run, and I've
gathered some more data that I'd like to share. I hope to be able to
devote a good number of hours to the bike this weekend.
I adjusted the idle screw (my service manual calls it a 'throttle
screw' - item #7 at http://www.bikebandit.com/partsbandit/showschematic.asp?dept_id=650201)
so that it would idle without holding on the throttle. That worked
pretty well for a few days, I let it idle for 15-20 minutes a few
times just to see if it could do that without stalling, and I also
went on a very short ride. In my adjustments of the screw, sometimes
the idle would go quickly up to 3000+ RPMS, and I'd cut the engine and
close the throttle screw a bit more.
Then this past Friday I went to fire it up to take it for a ride, and
it started up fine. I held on the throttle a bit to get it warmed up,
around 3000 RPMs. It started sputtering a bit, then there was two
very loud backfires - like gun shots. Then, it stalled. I then tried
to start it again, and it wouldn't start. I sprayed a little starting
fluid on the air filter, tried starting it again, and it backfired
again. This time I saw fire coming from the air inlet, it appeared
that the starting fluid had caught fire. No big deal really, it
burned up and the fire went out. The air filter was not damaged,
much.
So I let it sit until today, and I tinkered with it a bit. I made
sure that the battery was fully charged (I've got a battery charger
that I left attached to the battery while I was cranking the engine)
and adjusted the starter cable so that it was functioning properly.
Figuring that the only thing I really did was fiddle with the throttle
screw, I turned it all the way counter clockwise and then started
turning it back clockwise slowly until it would start. Finally, it
starts now, if I hold the throttle while pushing the start button.
Sometimes, although not regularly, when I'm trying to start it it will
backfire very loudly. Currently, I have to hold the throttle to keep
it from stalling. That makes sense to me, since I don't have the
throttle screw adjusted so that it will idle, only so that it will
start.
One thing that happens consistently is that once it's running and I'm
holding on the throttle at about 2000 RPMs, after running at that
engine speed for 1 to 1-1/2 minutes it will just stall. No backfire
or anything, it just simply dies on me. That has happened regardless
of whether or not I have the choke on.
So tell me, I have to clean the carbs this weekend, don't I? What
else should I check?
Albrecht via MotorcycleKB.com
>I adjusted the idle screw (my service manual calls it a 'throttle
>screw' - item #7 at http://www.bikebandit.com/partsbandit/showschematic.asp?dept_id=650201)
>so that it would idle without holding on the throttle.
Yes, that is the master idle knob that opens all 4 throttle butterflies the
same amount.
>That worked pretty well for a few days, I let it idle for 15-20 minutes a few
>times just to see if it could do that without stalling, and I also
>went on a very short ride. In my adjustments of the screw, sometimes
>the idle would go quickly up to 3000+ RPMS, and I'd cut the engine and
>close the throttle screw a bit more.
Will the engine idle without the "choke" on? You really don't have a choke on
those carbs. Instead of a flat plate in the mouth of each carb, there is a
small bypass that goes around the throttle butterfly.
There is a little valve that opens when you pull on the choke knob (or
operate the choke lever). Air going through the bypass sucks gasoline
straight out of the float bowls and the engine runs on that gas when the
"choke" is on.
But, if you turn the master idle knob up while the bypass valve ("choke") is
open, the idle RPM will rev up to 3000 RPM like you noticed.
Another possibility is that the engine starts sucking gasoline through the
three transition ports that are next next the the butterfly. That can cause
the engine to rev up as you described because it suddenly gets a lot of extra
gas which it normally wouldn't need at idle.
The transition ports get their fuel through the idle jet, and so does the
single idle mixture screw that is conceleaded under the EPA anti-tamper plug
on top of the carburetor, forward of the diaphrahm cap.
If you see the round EPA plug, nobody has ever drilled it out to adjust the
idle mixture screw, and there is a very good possibility that the single
outlet port is plugged up with gum and varnish.
>
>Then this past Friday I went to fire it up to take it for a ride, and
>it started up fine. I held on the throttle a bit to get it warmed up,
>around 3000 RPMs. It started sputtering a bit, then there was two
>very loud backfires - like gun shots. Then, it stalled. I then tried
>to start it again, and it wouldn't start. I sprayed a little starting
>fluid on the air filter, tried starting it again, and it backfired
>again. This time I saw fire coming from the air inlet, it appeared
>that the starting fluid had caught fire. No big deal really, it
>burned up and the fire went out. The air filter was not damaged,
>much.
Good thing you didn't set the motorcycle on fire. There are a few reasons for
backfiring. One is the simple ignition system that use two dual-lead ignition
coils for simplicity. Each coil fires two sparks at once. One of the sparks
ignites the cylinder that is coming up on compression, and the other spark is
a "waste spark" that fires into the cylinder that's coming up on the exhaust
stroke.
The waste spark will ignite any unburned mixture it encounters in that
cylinder, and the backfire will
come out the air cleaner because the cylinder that is at the end of its
exhaust stroke also has the
intake valve open, beginning the next intake cycle.
The engine can also backfire out the carburetor if the intake valves aren't
seating correctly because of carburized oil burned onto the backside of the
valves. That happens when the valve stem oil seals leak.
>
>So I let it sit until today, and I tinkered with it a bit. I made
>sure that the battery was fully charged (I've got a battery charger
>that I left attached to the battery while I was cranking the engine)
>and adjusted the starter cable so that it was functioning properly.
>Figuring that the only thing I really did was fiddle with the throttle
>screw, I turned it all the way counter clockwise and then started
>turning it back clockwise slowly until it would start. Finally, it
>starts now, if I hold the throttle while pushing the start button.
If the idle mixture passages and ports and jets were all nice and clean and
the
master idle knob was adjusted correctly, the engine would start when you
pulled the choke knob all the way out. You shouldn't have to turn the
throttle grip at all to get the engine to start.
Turning the throttle grip actually works against the bypass enrichener type
of "choke" that I described above, because opening the throttle butterflies
reduces the vacuum that the engine needs to suck
gasoline directly out of the float bowls.
>
>One thing that happens consistently is that once it's running and I'm
>holding on the throttle at about 2000 RPMs, after running at that
>engine speed for 1 to 1-1/2 minutes it will just stall. No backfire
>or anything, it just simply dies on me. That has happened regardless
>of whether or not I have the choke on.
That symptom indicates that the engine is probably starving for fuel because
the float valves are sticking. The alternative is that the engine gets so hot
the intake valves don't seat any more and the
engine backfires through the carbs for that reason. The carburized oil on the
valves that I mentioned above can cause the engine to stall because it can't
compress the fuel air mixture.
>
>So tell me, I have to clean the carbs this weekend, don't I?
It sounds like you just might need to roll up your sleeves and dive into the
carbs. You need a phillips head screwdriver that fits the screws on the float
bowls perfectly and doesn't twist out of the screw heads buggering them up.
Float bowl screws are very tight, and usually come loose with a clinking
sound. You have to push down really hard on the screwdriver while turning it
as hard as you can.
When you get the carbs all apart (you don't need to separate the carbs from
their brackets, just get the float bowls and diaphragm caps off), keep the
parts separate so they go back into the carbs they came out of. The float
valve *seat* is a brass doohickey that screws into the carburetor body and
the float valve (it's square or triangular) goes up and down in it,
controlling the fuel level in the bowl.
There may be a fine brass screen above the float valve seat (when the carbs
is upside down on the bench). Remove it for cleaning.
Spray your carb cleaner through every imaginable hole in the carburetor. I
have describe how to drill out the EPA anti-tamper plug and find the initial
factory settings for the idle mixture screws a bazillion times, so you can
google for "EPA anti-tamper plug" to get the instructions if you should
decide to
clean out the single idle mixture port under the idle mixture screw.
>What else should I check?
It would be nice if you could check the compression. If the compression is
very low, that may indicate crud on the valves. Intake valves that are very
tight when the engine is cold can also indicate crud on the valves.
--
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