I had posted before about my bike, once warm, not wanting to go above 1500 RPM.  After replacing the fuel lines, checking float height, checking the needles, rejetting with #40 pilots, adjusting the mixture and cleaning the carbs, I still don't know what the issue is.  Here are more details:

The bike will start fine, idle fine, rev fine, and generally operate flawlessly without any load on it.  Once on the bike, I notice a lack of power under 4,000 RPM, but it has enough to operate in traffic.  Above 4,000 RPM, the bike is a pleasure to ride, and it operates like it was meant to.  After about 3-5 minutes, the bike will give me trouble if I try to pull away from a stop.  Trouble means that it won't go above about 1,500 RPM.  At that point the bike will run very rough.  Adding the choke only makes it worse.  In another 30 seconds, the bike will no longer run.  Attempts to restart it will result in the bike idling at roughly at a low RPM for a second before dying.  Repeated attempts of this result in the bike not starting at all.  I've adjusted the mixture screws half a turn leaner at that point and the thing won't start. Adjust it half a turn richer, and it still won't start.  Oh, and the new plugs that I installed this week (well after the problem started) already are black.  Once the bike cools off, it'll start up fine.

I'm frustrated, and have no idea what is giving me trouble.  What are your thoughts?

And then, another clue:  Gas is currently coming out of the airbox of my GS, which has been sitting for an hour, left on prime.  I just turned off fuel flow at the tank petcock. 

Trouble when hot = rich.
You fit 40 pilots OK ... 1 point for you ...
But ...
Float height check ??
O rings check ??
You didn't do mains ??
Fuel over flowing into airbox ?? <--------- ah ha ... you lose 3 or 4 to 1.
Unknown crap clogged ??

I can of course go over it. Send you pics and let you know what is wrong where ... and if tank or other stuff is to be checked.
Cool.
Buddha.

I had a similar problem, it was my signal generator, how many miles are on the bike, they seem to go out at about 25000

Quote from: The Buddha on September 12, 2008, 08:17:23 PM
Trouble when hot = rich.
You fit 40 pilots OK ... 1 point for you ...
But ...
Float height check ??
O rings check ??
You didn't do mains ??
Fuel over flowing into airbox ?? <--------- ah ha ... you lose 3 or 4 to 1.
Unknown crap clogged ??

I can of course go over it. Send you pics and let you know what is wrong where ... and if tank or other stuff is to be checked.
Cool.
Buddha.

Float height is within spec. 
O rings are in place.
I didn't do the mains, but the thing runs great when the RPMs are up. 
Nothing should be clogged.  I cleaned the carb, which was already fairly clean.  I also added a fuel filter at that time. 

Would a signal generator cause fuel to leak out of the airbox? 

Juan1, I had the same problem before.  You may want to check your needle valve and valve seat assembly.  If the needle is worn out, thus reducing its ability to keep the fuel out from the float chamber consequently it would be the same if the valve seat o-ring is not up to specs - may look good visually but not functionally.  So having both scenarios mentioned the fuel would just keep going into the float chamber and out thru the main jet and pilot jet, however, since the jet needle is in place blocking it's way fuel then go thru where there is of least resistance thru the pilot air jet (x2) and dumping it into the lunch box.  I hope this make sense.  Good luck.

sounds like you have a blocked tank vent in the fuel cap, when your bikes only got about a quarter of a tank of fuel, try doing a run with the fuel cap not done up (put a bit of tape across the top of the tank to stop it sloshing everwhere) and see if that makes a difference

You need to be able to get air into the tank to replace the fuel being used, if you dont, your bike will start to play up after a few minutes of riding, and when you stop, the tank will pressurise if the air cant get out and it will flood your carbs when you are stopped

IanP - Blocked tank vent will not get the fuel flowing out the airbox. Its prolly a high float, or bad O rings - like davegs said.
Cool.
Buddha.