Cylinders won't work together before 4k RPM.

[C Squared]

So my 1990 GS has decided to only run on one cylinder. The strange part is that it will run on one OR the other but not both at idle. If I pull the left plug boot, the right cylinder will start and run. If I pull the right plug boot, the left cylinder will start and run. But when both plug boots are on one will fire and run but not the other. Upon pulling the plugs the electrodes look white as the bike is running lean.
BUT:
Upon riding both start to fire and run fine after 4k rpm or so. 

What's the deal?

TIA!!!

[C Squared]

Switched out the coils... no change. 

[coll0412]

Is there any change in how well it runs when you pull one plug wire off, basically does one cylinder run better than the other.

My thoughts is that maybe it a carb sync deal

[C Squared]

They run the same, neither seems to run better than the other. Weird.

[treybrad]

Could it be an issue somehow w/ the vacuum at idle not pulling enough gas to the carbs? This could result in the white-ish plugs, once the motor spins up a bit, the vacuum kicks up the suction and it runs better?

I never had any problems w/ my frame mounted petcock, does this sound feasible to anyone? The white plugs make me want to think it's a fuel issue more than anything. We've gone through the carbs (twice..), and they are clean and properly jetted.

trey

[treybrad]

and, if it helps at all. Before we swapped out coils, with one of them you could pull a plug boot and if it was within 1/2" or so of the cooling fins it'd arc across the gap. We swapped them out and now neither will do it, but.. is the arc-ing a sign of a bad boot? Worn down insulation? Or are the new (used) coils not creating enough spark to arc?

trey