Huygens, I am the one who posted the "flow rates" for fuel flow with & without vented gas cap. I am using the stock petcock & the same size rubber tubing as stock (just better quality !). My bike has a K&N filter in a yamaha billet airbox, no AIS, no fuel pump and, until recently, modified stock exhaust. It'll wrap the speedometer even with the windshield on. I suspect that one of two things is happening to you. Either

a) as Doc suspects something in your main jet "circuit" is not right. This is the circuit of the carb that comes into play from about 3/4 throttle to full throttle. It is not so much a matter of RPM as throttle position. If you keep the bike under 3/4 throttle will it eventually hit higher speeds ? Does it display the same problem in lower gears, or just 5th ? Can you run it right up to near redline & hold it there in a lower gear without fuel starvation ? How do you have the fuel line run ? Is it directly from the petcock to the carb & is it reasonably level ? If you remove the drain screw from the carb does the fuel run out ? If you remove the bowl does the fuel run when you drop the floats & stop when you lift them ? Are the screws on top of the carb tight, & is the rubber diaphragm seated properly ? Is your main jet completely drilled through (don't laugh, it's happened). Is the needle jet installed properly ?

b) Something else is messed up that is fooling you into chasing a carb problem that may not exist. How old are the plugs ? Do you have good spark ? Do you have any air leaks or open hoses ? How is the oil level ? Too much oil can cause weird problems at higher rpm's. If you changed the air box, are you sure you removed/capped/replaced all the hoses, etc. Check everything over to ease your mind and confirm that it's a carb problem.

I once chased a similar problem for a month in my GSX-R1100, only to eventually determine that the spark plugs were to blame. I almost drove myself crazy !! If you think it a pain taking off one carb, try pulling FOUR CARBS out 20 or 30 times !! It's enough to make you insame . . . . . sorry . . . it still hurts . . . .

Rup