I thought I had it beat, but my left cylinder still won't fire when cold.  I've adjusted the valves, rebuilt and rejetted the carb (all new o-rings), adjusted the float height for the ideal fuel level, and balanced the carbs, but it just won't run right.  My only theory is a possible vacuum leak.  The intake boots seem to be in great shape, so maybe it's the petcock or petcock line.  The petcock is pretty crappy (leaks out of the valve), but the diaphragm is in good shape. 

Anyway, before I give up, does anyone have any recommendations on what I should use to seal all possible sources of air?  I have some permatex non-hardening gasket sealer (willl work okay for the petcock).  What should I use for the boots? 

Arrgh!  This is driving me nuts.   

Could be a coil problem, I had a GS1100E that did that.  Bad coil.

Good idea.  I'll switch them and see if it makes a difference.  It will shock the crap out of me, but it could still be bad.  I've been stuck in the fuel system paradigm too long to even think about the electrics. 

I'm having the same problem... Someone on here had mentionned to check the secondary ground.

Sounds electrical, keep hunting.

Try removing the left cylinder wire and testing for a spark.  It should be bright white or blue, and jump at least a 1/8" gap.  

Loose boots are difficult to seal.  Silicone won't stick, and most adhesive-type sealants will stick it together for good.  If you can't cinch it up tight with a hose clamp I suggest you replace the boot.

Quote from: GeeP on May 17, 2006, 11:04:29 PM
Sounds electrical, keep hunting.

Try removing the left cylinder wire and testing for a spark.  It should be bright white or blue, and jump at least a 1/8" gap.  

Loose boots are difficult to seal.  Silicone won't stick, and most adhesive-type sealants will stick it together for good.  If you can't cinch it up tight with a hose clamp I suggest you replace the boot.

Would an Electrolyte Silicone work? make and electrical passage instead of adhering...

Cap off the vacum line nipple on the left carb and run the bike in prime.
If that doesn't help then the vacum line wasn't the problem.

(well I suppose it could be one of many, but that seems unlikely)

Electrical wise you could easily swap parts from one side to the next and eliminate things very easily. Have you taken a compression check to eliminate a base engine concern? I have seen in cars where a valve will stick when the engine is cold but be fine as it gets warm. All it takes is a tight guide.

I have tested the compression, and it is within 20 kPa between left and right.  Since it was tested when the bike had only idled and the left cylinder wasn't running reliably, I'd say that they're close enough to equal. 

I have a spark tester, and both sides have produced spark at the 20000 V setting.  While I will exchange the parts to eliminate this possibility, it seems unlikely to me, though certainly possible. 

I have tried capping the vacuum line by clamping it closed.  It didn't seem to help, but I'm running out of ideas....

I'll let y'all know how it goes tonight.  I have to w-o-r-k today so I won't be able to do anything until this evening. Thanks again for your ideas.  Hopefully one of them will work.

When you checked your valves did the buckets rotate smoothly/easily in the head?  I remember someone (GSJack?) mention a sticking bucket that caused problems until the engine warmed up and the fit loosened.  Seems like a long shot but worth a try.  Also, didn't Kerry have a long-running issue with one cylinder mis-firing that turned out to be electrical?  Might want to run a search on that one.

-M

I4

If its fine when hot and bad when cold may be too tight valves or a bad choke ... open when closed or closed when open
Bad in 1 cyl all the time = aux ground but may clear with revving.
bad in 1 cyl all the time and definetly clears with revving = vacuum leak, but wd40 it first and eliminate it.
Cool.
Srinath.

Wouldn't tight valves make problems worse as they warm up?  You know, tight when cold -> don't close completely when hot.

Not quite ...
Not close when cold will close when hot within reason ... as in if its not that much negative. The head made of aluminum expands more tha the valve which is steel ...
Of course you go more negative and it will not close hot either.
Now warm up is worse cos the valves get hotter faster than the head ... so you can have a case where its tightish ... but not negative when cold, to negative when warming up and back to closing when hot.
Cool.
Srinath.

I thought I should update the status of the mystery.  So I decided to recheck everything before continuing.  The first thing I checked was the fuel/float level.  Remember, I already set the float heights about 3-4 weeks ago.  They were way off.  Left was extremely rich, right was lean.  WTF?  I know I switched the floats the last time I had the carbs apart (for soaking in B12), and checked them to find them way off.  I switched them back, checked the levels, and they were perfect.  Why would the fuel levels be so off?

Quote from: seshadri_srinath on May 18, 2006, 12:05:19 PM
Not quite ...
Not close when cold will close when hot within reason ... as in if its not that much negative. The head made of aluminum expands more tha the valve which is steel ...
Of course you go more negative and it will not close hot either.
Now warm up is worse cos the valves get hotter faster than the head ... so you can have a case where its tightish ... but not negative when cold, to negative when warming up and back to closing when hot.
Cool.
Srinath.

Srinath, a question you might be able to answer.  the reason I believe(d) the opposite is because I was told so by another bike mechanic (of unknown quality), but also because I have valve noise when hot.  My valves were recently adjusted to within spec (and I cranked the starter quite a bit to displace any oil).  This got rid of my valve noise when my engine was cold.  However, it comes back once the engine warms up.  Now, I assume that with tight clearances, the tapping noise is caused by the shims hitting the cam lobe.  So this would mean that my clearance decreases when the engine is hot. 

So am I wrong?  If so, what is the correct explanation?