Firing on one cylinder during idle and low RPMs

[jh23j0b]

I need help. I have had the carbs apart a couple of times and believe the idle and slow passages are clear, but still idles on only the RH cylinder. The LH cylinder starts firing around 2000 to 3000 rpm. Both plugs are sparking at idle. I'm about ready to tear into the carbs again just to make sure the idle circuits are clear. There seem to be a lot of topics related to this. Has anyone actually ever solved this problem?

[Mdow]

how do you know its only on one cyl?

[jh23j0b]

two observations: 1. I can hear it and feel it, 2. the LH pipe is warm and the RH pipe is hot during idle

The LH cylinder starts firing once I get it up to about 2000 to 3000 rpm

[jh23j0b]

One more observation: When idling and I plug off the idle air inlet jet with my finger on the LH carb, nothing happens; when I take my finger off, it jumps up a few hundred rpm for a second. When I plug the RH idle air inlet jet, it stalls.

[the mole]

With that last observation, it has to be a blocked idle circuit in the L carb. When you block the air inlet, the suction gets fuel in the circuit, when you let go the L cylinder fires on that fuel and the rpms jump up, then the fuel is burnt and it dies on the L again. If you block the R one the motor dies as neither cylinder is firing...the L one because of lack of fuel, the R one lack of air (too rich).

[jh23j0b]

Since my last post, I have removed the carbs, removed the float bowl and confirmed that the passages are clear using carb cleaner. I can see light thru the pilot fuel jet. I can blow carb cleaner and compressed air thru the pilot air jet and it exits thre the holes in the carb near the throttle plate. So it seems both the air and fuel jets/passages are free flowing, right?

[the mole]

Sounds like its clean. Sorry I can't be more help as I'm not familiar with working on these carbs. Last GS I had to work on was a GS450S in about 1982! My '07 just keeps going.


Hey, just had a thought, could you be getting too much air in the L carb due to a leak in the petcock vacuum line? (not even sure which carb that goes into?). Could try plugging the vacuum spigot at the carb and running the tap on PRIME while you test it.

[jh23j0b]

Tried the plugging the vacuum port suggestion and no difference. Swapped vacuum diaphrams too - didn't help. Doesn't seem to be a vacuum leak.

While idling, plugging the pilot air inlet jet, revs go up to 3500-4000 with both cyl firing seemingly fine.

While idling, partially plugging off the plastic slide opening seems to create enough vacuum/velocity to pull air/fuel thru the pilot circuit and I can for the first time hear it idling on both cylinders. Could there be a problem with valve mal-adjustment causing poor vacuum at idle?

[jh23j0b]

Checked valve clearance and all within specs. Put back together and still runs the same: LH cyl not firing on idle and up to 3000. LH and RH cyl firing past 3000.

Is this electrical? I checked resistance of the signal coils and they were approx 340 ohms.

Also, I swapped the plugs and still runs the same.

[DoD#i]

Try swapping the coils side to side and see if it follows one coil?

[jh23j0b]

Good idea. I'll do it tomorrow - I have come in for the night to work on divorce paperwork.

[Ronin]

Had the same exact problem this spring.There is a small valve under the front and underneath the float.It's the inlet for the fuel coming into the bowl.I changed the coils back and forth and alot of other things.....

Take off the float,find the inlet to the front.take out the little valve.Check for crud there.There may be none,as was the case with mine.The hole the valve sets in must get varnish in it and cause a sticking condition.The valve must be able to move freely up and down.

I took a piece of cloth and polished the inside of the barrel the float sits in,and ran a small wire the short distance.Popped it back together and bingo fuel in the bowl.

I'd be willing to say if you opened the bowl outlet drain with fuel in it,only a trickle would come out.

[EzTargut]

My bike had the same problem.

would idle on one cylinder until about 3k then run decent.

It turned out that the petcock was leaking fuel through the vacuum line into the left carb.
Pull it off the left carb and see if fuel leaks out while toggling petcock.


split the tube in half and put a bolt in each end and ran on prime for a quick fix. Eventually got a new petcock w/ out a vacuum feed it was like 27 bucks and the things somewhere around here.