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Bike runs great on side stand, sputters and dies when it leans right

  • Thread starter Thread starter cp___32
  • Start date Start date
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cp___32

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As the name suggests, the bike runs decent when on the side stand. It revs strong and idles well. When I straighten the bike up it doesn't run as great. There's some popping and bogging at low RPM. When I pitch the bike right (not under load) it stumbles and dies. If I lean it back to the left quick enough it'll come back and run good again.

Petcock is set to horizontal. Carbs have all been cleaned and new o-rings installed. Floats all set and verified that all float needles work properly. Bench synced and then vacuum synced. Fuel tank is more than half full and there should be no issues pulling fuel down to the carbs with the amount in the tank, besides the float bowls should have more than enough fuel to run the bike for a few seconds at the very least.

Any ideas what might be causing the issue?

I was really hoping to take it out for the maiden voyage tonight as I just bolted the license place on it when I got home from work.

Thanks
 
What is your oil level with the bike upright, not on either stand? Just guessing, my mind is a blank right now.
 
Is there enough fuel in the tank??? You may also have a loose wire that may be causing problems too when you lean your bike from one side to the other.
 
Petcock issue I would guess. It runs good while leaning on the side with the petcock angled and down. Vacum hose from petcock to carb fowled some how when up right messing up gas flow.
 
Thanks for the replies.

Oil level is actually a touch high maybe by a few mls. I'll drain some out just to be sure.
Fuel level is over 3/4 of a tank. No fuel line isn't getting pinched when the bike leans nor is the vacuum line. I'll likely unbolt the tank and have someone hold it level while I tilt the bike and see if I get the se symptom. That should tell me if it's tank related or something else.

I find it difficult to believe it would be starvation cause the effect is almost immediate when I pitch the bike. Within 5 seconds it will die if I lean it on the same angle as the side stand but in the opposite direction.
Also I have checked multiple times since it's been running for vacuum leaks around the carbs. With new boots and o rings al around it's sealed up good.

An odd symptom that might be related but might not be. I checked all 4 wires for spark by disconnecting and using a spare plug. All were good. When I wanted to check if all cylinders were firing if I unplugged the plug wire from 2 or 3 the bike would stumble badly but from 1 or 4 it didn't change how it ran much at all. I can't recall but I believe I did that while sitting on the bike so it was vertical. When it's vertical I get popping and poor throttle response at low range and a bit of hesitation till about 2500 rpm.

I'll check voltage to the coils as I pitch the bike too and see if anything interesting happens
 
Update:

Took the battery out and put it on the ground and ran jumper cables to the bike to eliminate the possibility it was something to do with the battery acid sloshing around. Still sputters and dies when it leans to the right.
Lifted the tank up and held it level while angling the bike side to side, same result. It dies.
Removed the tank completely and ran off the previously mounted aux fuel supply (a funnel and a long hose). Same result.
Checked voltage at all sorts of angles of roll. No change in voltage.

So the only thing that seems likely at this point is that a the float on one of the two left hand side carbs are set incorrectly. When the bike is rolled to the right, the fuel flows to one side of the carb and the Venturi can't pick up fuel so the cylinder runs lean then starves.

Is there an efficient way to check/adjust the floats with the carbs in situ? The only way I am aware of is using a micrometer with the carbs off the bike but I was hoping there was a way that didn't involve me taking the carbs off again.

Otherwise, any other thoughts on what it might be or does it sound like I'm on the right track?
 
Try doing the test in the dark. Spray the plug wires and caps with a water spray bottle. Any arching from the plug wires or plug caps ? Id change the caps, if you haven't in a while, just for good measure.
 
cp___32 said:
Is there an efficient way to check/adjust the floats with the carbs in situ? The only way I am aware of is using a micrometer with the carbs off the bike but I was hoping there was a way that didn't involve me taking the carbs off again.
Click to expand...

Yes, you can check them but you can't really fix anything with the carbs in place. It will tell you if you need to fix anything in there, and it's what I would check next. You check the fuel level in the bowls with the engine idling. I always check it if there are carb problems I don't understand, quite often it's goofed up somehow. Look up the Fuel Level check in the Suzuki Service Manual, it's easy and can be done with home made tools.
 
Not sure leaky plug caps would get worse when the bike is tilted but I haven't been entirely happy with the new NGK caps that I installed anyway. Any suggestions on an alternative? I think those might have been the only ones my local shop could source and that might be why I ordered them. It was a few years ago now so I can't remember.

Wouldn't hurt to do that check anyway so I will. The wires and harness are definitely not moving at all when I tilt the bike I've got the harness pretty well secured.
 
cp___32 said:
Thanks for the replies.

Oil level is actually a touch high maybe by a few mls. I'll drain some out just to be sure.
Fuel level is over 3/4 of a tank. No fuel line isn't getting pinched when the bike leans nor is the vacuum line. I'll likely unbolt the tank and have someone hold it level while I tilt the bike and see if I get the se symptom. That should tell me if it's tank related or something else.

I find it difficult to believe it would be starvation cause the effect is almost immediate when I pitch the bike. Within 5 seconds it will die if I lean it on the same angle as the side stand but in the opposite direction.
Also I have checked multiple times since it's been running for vacuum leaks around the carbs. With new boots and o rings al around it's sealed up good.

An odd symptom that might be related but might not be. I checked all 4 wires for spark by disconnecting and using a spare plug. All were good. When I wanted to check if all cylinders were firing if I unplugged the plug wire from 2 or 3 the bike would stumble badly but from 1 or 4 it didn't change how it ran much at all. I can't recall but I believe I did that while sitting on the bike so it was vertical. When it's vertical I get popping and poor throttle response at low range and a bit of hesitation till about 2500 rpm.

I'll check voltage to the coils as I pitch the bike too and see if anything interesting happens
Click to expand...
You unplugged the spark plug wire from #1 and #4, one at a time i'm guessing. and it didn't make much difference? It should because it's running on 3 cylinders. If it is hitting on all four before you remove one. This is an odd problem. I'm thinking carb problem. Electric is either on or off. Not a lot of sputtering. just my experience but anything is possible keep checking and tracking down stuff. It's not magic, something is up.
 
I have seriously just about had it with this bike.
I took the carbs off and readjusted all the floats, put them back on and I have the same issue.
I am getting spark at all four cylinders. Checked and there is no spark leakage doing the spray bottle test. I was using a funnel with plenty of fuel to eliminate the petcock or a plugged tank. Carbs were just cleaned and rebuilt. Brand new gasoline.
There is nothing I can think of that changes between running on the side stand and leaning the opposite way except fuel flow but if the floats aren't to blame then what? I really can't keep throwing new parts at this thing. Besides most parts on the bike are new now and I am not going to just start replacing new parts with other new parts and hope I luck into a solution.
 
from your description, it really doesn't sound like a carburetion issue to me.

Not having any change when removing #1 or #4 points strongly at that coil, ignitor, or both. Loose connection of some sort that rotates out of position when leaned to the right? Alternatively, maybe when it is leaning left, a connection is being made.
 
I would check inside the points cover and see if anything is loose. I know you don't have points, but I would take a look. I would also lean the bike over to the right and check every wire that has to do with making the engine run with a multimeter or test light, if a electrical connection is not being made or weak it should show up.
 
You may have done it already, but I didn't see it mentioned above.

Have you shot a spray or two in starter fluid into the intake while it's stumbling, just to verify that it is, in fact, a fuel issue?

It definitely sounds like it is fuel issue to me, but before you drive yourself mad continuing chasing down that rabbit hole, I'd definitely want to make sure it wasn't a loose wire or some other unknown.

Your process of elimination seems sound so far. You've got to be almost there!
 
If the lighter fluid makes little difference, and you suspect it's electrical, I might check by wiggling wires 1 & 4. If disconnecting plug wires doesn't seem to affect the engine, then they may not be operating correctly in the first place.

I don't think the wire's weight would be enough to be affected by tilting, but I'm wondering if contacts that were dirty on one side might be affected somehow. How do the plugs on those cylinders look?
 
I have a few spare aftermarket drain plugs for the carbs from the rebuild kits so I am going to make a measurement tool and see how things change when I tilt the bike. I was hoping to read the plugs by doing a plug chop of sorts once the bike does but I am not sure how long it takes to see evidence of how the bike is running once it starts dying.

Im hesitant to go away from the notion it is fuel related since a poorly running engine could cause weak spark once it starts stumbling. The could were new from about 6 years ago and other than the last few weeks of firing it up to tune the carbs they and the plugs and caps have seen no running. I don't particularly like the NGK caps but might change those to something that seats a little more solid but they should do the trick since I am getting reasonable spark.
I'll try tilting the bike and probing around while it's off and then see if anything jumps out.

Nothing seems ems to flex enough to cause a leak on the boot side of things but I will check that again with some quick start to be sure. I might throw the carb tune on there again and see if anything jumps out. It would be good to identify once and for all what cylinder is giving me grief. I've never heard an old gs run so I don't know if mine sounds bad or not. Phone speakers and YouTube don't do it justice.

Ill do some more checks shortly and report back.
Thanks again for all the help (and encouragement) :)
 
Pulling a plug wire and it having no effect is a diagnostic test for a non firing coil. Assuming this is the case. Swap the ht leads from the coils to the other pair of cylinders i.e. swap 1&4 with 2&3. Now see what's what when you again pull spark plug caps. If the motor now stumbles on 1&4 you have found an ignition problem with one coil.
If that turns out to be the case the likely suspects are the coil supply plugs, and or the ignitor plugs.
 
I kinda skimmed through this. If it were me I think I'd recreate the situation (and I didn't have a IF heat thermometer... which I do), then pull each plug and look to see if one or more looks different from the rest. If it is somehow a coil or if it is going rich on one cylinder, that plug should appear wet. If it is going lean (maybe a boot leak when the weight shifts or something, or a low fuel level) then one of the plugs may be whiter than the rest.
Now if I actually did it, I'd probably start by using my IF Thermometer and see if I had a cold cylinder and just pull that plug. Then Id concentrate on that cylinder, coil, plug, wire, carb, etc...
 
Brendan W said:
Pulling a plug wire and it having no effect is a diagnostic test for a non firing coil. Assuming this is the case. Swap the ht leads from the coils to the other pair of cylinders i.e. swap 1&4 with 2&3. Now see what's what when you again pull spark plug caps. If the motor now stumbles on 1&4 you have found an ignition problem with one coil.
If that turns out to be the case the likely suspects are the coil supply plugs, and or the ignitor plugs.
Click to expand...

does this work? I know you can switch 1 with 4 and 2 with 3 because it's a wasted spark system but wouldn't you be firing at the wrong time if you switched 2 for 1 or 4 and then 3 for the other?
 
Because I didn't feel like pulling the carbs....again.... I checked spark. I found two issues. One is simple, but the other one not so much.

Used a spare plug to check spark on all 4 cylinders (just while cranking, there's no fuel in the bike currently). Propped the bike up on the bad side and checked spark. First I checked 3. Super strong spark. 4....one initial flash then nothing. I put the bike over on the side stand and checked again. Spark comes back. Put it in the middle. Weak, and intermittent. Back to the bad side and it goes away completely.
Swapped the feed cables for the coils and the problem moves to 3 and 4 works like a champ. Switched things back and checked voltage and resistance. 3.6L and 3.9R which seems good, but now for the one strange thing. Voltage was 11.59 on the right at the molex connector just ahead of the coil, only 10.2 on the left. I disconnect the left coil and the voltage jumps up to battery 11.59. Plug it back in and voltage drops. Checked continuity on the wires and found that I have an intermittent open on the O/W wire on the side that's malfunctioning.

Now, I get that I have to replace the wires to the coil. That's a no brainer. But I zip tied them to the frame and tried the tilt test again and still found that I lost spark when tilting right. There's no voltage or resistance change when I tilt so it must be something upstream. My next stop is going to be chasing those wires back to the signal generator. So Mike10....sounds like you're onto something. I'm pretty weary. Been working 50+ hour weeks and just came off back to back 12s so I'll give the brain a rest and dive into the side cover tomorrow.

You guys will have me up and running yet....

Thanks :D
 
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