Motorcycle Repair: carburator overflowing, gravity flow, needle valves

Question
i have a 1993 yamaha secca 2 600,  the problem is my #1 and or #2 carb overflowing, i had a bike shop check the carbs for me, they said they found a faulty o-ring and the diaphram was un seated in the #1 carb, I re-installed the carbs and the bike did ok for the first hour, then the #1 or #2 carb starting doing the same thing, overflowing again, took the carb back, ask the mechanic to check the #2 carb and they said it was fine. they are trying to say my problem lies in the fuel pump (too high of pressure), arent i correct in the assumption that the float in the carb should be regulating the amount of fuel into the bowl?  i cannot see how the pump could cause this condition, my gas flow is normal, i even by-passed the tank and pump and used a gravity flow bottle to supply fuel, thus eliminating the pump, ...same problem. i realize the 1 and 2 carbs share an overflow, so i am not sure if its in 1 or 2 causing this problem, any suggestions.      Note, i am mechanically inclined to do this repair myself, i am an appliance tech and do all my own auto repair, so any help would be appreciated.                   thanks, steve     stevnray1972@yahoo.com

Answer
Hi Steve,

My money is on you, pal. I believe that your diagnosis is more accurate than the mechanic's. Fuel or head pressure isn't a problem with this system. Rather, likely one of the following:

Common causes for over-filling of float bowls:
1) varnished carburetors & needle valves (aka float valves)
2) worn needle valves and valve seats
3) debris (rust) caught between needle valve and seat
4) float heights improperly adjusted

I'll send a  couple tech information files to your email addy. Keep me posted on your progress via email.

Respectfully,
Mark Shively