1 Cylinder not always firing at idle

[Jim R]

1982 GS1100G, all original parts.

Newly rebuilt carbs last year with all new jets and gaskets etc.

Bike ran great after rebuild.

Stored the bike over the winter with Seafoam mixed with gas in the tank.

Started right up last week but Cylinder # 2 (2nd from the left if you are sitting on the bike) is not firing when at idle.

When starting out in first gear, I can feel it kick in at around 3000 RPM.

When I start the bike cold, The exhaust header barely gets warm when left idling.

Spark to that cylinder is good.

I have the air box off and am hoping someone knows a trick to get the fuel flowing to the combustion chamber before I take everything off and take that carb apart again. It's a real bear to get back on.

Help?

 

[hillsy]

You're saying the spark is good but it's pretty easy to make sure of this first up. Swap spark plug leads between 2 and 3 and see if the problem moves to the other cylinder. If so, it's the lead / plug cap. Then swap spark plugs over and check the same.

Far easier to completely rule this out first before you start digging into the carbs - although it does sound like a blocked idle / pilot circuit.

 

[Jim R]

You're saying the spark is good but it's pretty easy to make sure of this first up. Swap spark plug leads between 2 and 3 and see if the problem moves to the other cylinder. If so, it's the lead / plug cap. Then swap spark plugs over and check the same.

Far easier to completely rule this out first before you start digging into the carbs - although it does sound like a blocked idle / pilot circuit.

I pulled the plug and started the bike with the plug still connected to the lead. I can see the spark clearly.

 

[storm 64]

I'd just take it out and run the heck out of it for about 100 miles. That should fix it.

 

[Jim R]

I ran it good and hard for about 20. It's annoying that it wants to stall at idle. I'm looking for an easy fix instead of taking the carbs off.

 

[storm 64]

How about a new set of spark plugs, fresh fuel. Turn the idle up so it don't stall at red lights. Double check your battery voltage... valve clearances.

 

[fededevi]

The second cylinder is the one with the vacuum thing for the petcock? Try to remove the hose from the petcock, set the petcock on prime, close the hose with your finger and start the engine.
I had trouble on my 750 on the second cylinder misfiring and burning spark plugs and the problem was the petcock leaking air into the vacuum line. The effect was obviously more evedent at low rpm.

 

[Guest]

After you rebuilt the carbs, did you do a vacuum sync? With everything else set perfectly, that carb could be closed a bit more than the others. As you open the throttle, it opens up with the rest of them, although just a bit less, but not quite as noticeable.

Could also be a little bit of crud blocking a jet.

The 1100G is not known for having difficulties getting the carbs in and out. Probably ranked #3 after the 850 and 1000G. If it's hard to get the carbs seated in the boots, it's probably time for new boots.

 

[Jim R]

The second cylinder is the one with the vacuum thing for the petcock? Try to remove the hose from the petcock, set the petcock on prime, close the hose with your finger and start the engine.
I had trouble on my 750 on the second cylinder misfiring and burning spark plugs and the problem was the petcock leaking air into the vacuum line. The effect was obviously more evedent at low rpm.

I'll give that a try. Thanks.

 

[jdvorchak]

Could also be that vacuum line has a crack in it allowing it to suck air. Although in my experience if not the vacuum hose it's a plugged idle jet/passage. Although that would be rare only sitting over the winter. I would think it would take a year for that to happen. Hope it's vacuum related.