My '91 GS500 has a hard time starting now and the right cylinder does not fire if the bike starts at all.  I adjusted the float height, but it did not stay at the level it was adjusted to. It only starts with full choke and often cannot idle very long before it dies. Without the choke, the engine dies. Also, the exhaust spits out white smoke.

Here's what I've done in the past two days:

I have put in new intake pipes between engine and carbs, new rubber airbox boots, a new air filter, new spark plugs, new oil & filter. There's fresh gas in the tank.

I adjusted the idle screw to the proper setting.

Then I checked the float height using clear tubing and the carb drain. Left carb was fine, right carb was below the gasket.  Adjusted the right carb to the proper float height, put everything back together and the engine started right up and was firing on both cylinders. Choke was good, engine warmed up and then engine idled normally, the throttle was responsive, everything was peachy for a good 5 minutes or so, and then rpms slowly dropped and it died.

Now it barely starts if at all, and it only fires on one cylinder. Pulled out the spark plugs, both look normal. I checked the float height on the right carb again, and it was low, the same place before it was adjusted. Any ideas on what I should do/try?

The carbs were rebuilt 6 months ago (new bowl gasket, o-rings, float needle and seat assembly), though I did let them sit for the last 6 months without any gas inside of them. When I opened the right carb to adjust the float height, the bowl was still pretty clean.

Auxillary ground. If all the carbs and valves are good. In fact I'll check that first. Also see if crank trigger is good.
Cool.
Srinath.

Leaky float in the right carb? 
Maybe the float, needle vavle, or the hinge is binding?

Below the gasket - how far low. A bit low and it should still run atleast at idle.
I actually think its crank trigger. Works fine when cold and dies on 1 when warm (and warm isn't absolute) you can have 80 degrees outside and it may be too warm for it to even start on that cyl, and at 40 it will start and run till the crank trigger gets to ~80 degrees. Its a electronic gizmo inside that sealant and when warm its internal resistance can be high enough to take the bite out of your spark and not run. it cannot be caught with naked eye. It will get worse and quit on that cyl permanently and it will actually run OK at high rpm if you can get it revved high enough and never let it drop.
My 89 used to run ~20 mins and then die on 1 cyl in the begining of this problem. I'd start it and jump on an open stretch of the highway and manage 15+ miles before it will quit on 1 when I slow to take the off ramp. Had I stayed WFO, I'd have made it another 100 miles presumably. But that probably made it fail very very rapidly. In a few days it was not running on 1 cyl at all and I knew it was the trigger by then.
Its on the right side behind the advancer. Round plate with wiring comming out of it.
Cool.
Srinath.

Thanks for all the replies and help 

I didn't adjust the float height when I rebuilt the carbs. When I first checked it yesterday it was about an inch low, I adjusted it to the gasket height, and then after running it went back to an inch low again.

I did check both floats when I rebuilt the carbs by dunking them in water, no bubbles. They are, however, stained a rust color. Could there be a leak I couldn't see? I'm also wondering if the new needle and seat were no good to begin with since I bought cheap aftermarket parts. Can I switch the float, needle and seat from right to left to see if there's a problem?

Two days ago, I thought I had fixed the bike since the carbs were cleaned and I fixed a vacuum leak. I didn't realize it was running on one cylinder since it runs so smoothly. It started up easily and I noticed the speedometer and tachometer illumination lights were not working. I hadn't ridden bike at night before. and figured maybe the bulbs were burnt out.

I took it for a ride (with the choke on the entire time, the engine wasn't warm yet) and went two blocks before the rpms slowly went down and the bike died as if I were running out of fuel. I switched to reserve and the bike fired right up again. I rode another block before the bike died again, this time it just cut out suddenly and the speedometer illuminated at the same time. Could this be a symptom of the crank trigger?

When it's running on one cylinder, I can rev it up to keep the engine alive, but if I open it up too fast it will always die. And by too fast, I mean normal acceleration or faster, so I have to go pretty slow.

That sounds like a classic case of "I didn't turn the petcock back on" to me.

Yup I tend to agree ...
Cool.
Srinath.

Clarification: tank petcock.

Quote from: Egaeus on May 08, 2007, 11:53:35 AM
That sounds like a classic case of "I didn't turn the petcock back on" to me.

Hehe. I thought I might not turned the screw all the way, but I checked and it was fully on.

Quote from: joy on May 07, 2007, 09:13:58 PM
My '91 GS500 has a hard time starting now and the right cylinder does not fire if the bike starts at all.  It only starts with full choke and often cannot idle very long before it dies. Without the choke, the engine dies.  Also, the exhaust spits out white smoke.

Water in the gas?  Also, I suspect a clogged airjet; one or both in the mouth of the carb.

Quote from: joy on May 07, 2007, 09:13:58 PM
I have put in new intake pipes between engine and carbs...

Did you replace the o-rings between the intakes and the carb boots?

Quote from: joy on May 07, 2007, 09:13:58 PM
Now it barely starts if at all, and it only fires on one cylinder.  Pulled out the spark plugs, both look normal.  I checked the float height on the right carb again, and it was low, the same place before it was adjusted.  Any ideas on what I should do/try?

Does the float pivot smoothly and easily on its shaft?  Does the float needle slide smoothly in the needle seat?  Is the seat notched in its circumference from the brass body of the needle?

Quote from: joy on May 07, 2007, 09:13:58 PM
The carbs were rebuilt 6 months ago (new bowl gasket, o-rings, float needle and seat assembly), though I did let them sit for the last 6 months without any gas inside of them. When I opened the right carb to adjust the float height, the bowl was still pretty clean.

Was the gastank full/no room for condensation?

this sounds a lot like the problems i have been having.