hey, i'm new on the board, and i have a problem i was looking for some input to. i have a gs450l and it just won't run right, i had to put in a used engine, i set up the timing and did the valve shims to the specs in the repair manual, but when it starts (very hard starting) it seems like it's starving for gas, even with the petcock in the prime position. it also heats up extremely fast. if i put my finger over the upper opening on the intake side of the carb the bike starts to run better for a split second, but then sputters and dies, (the upper diaphram opening). i am at a complete loss, it does seem like a vac. leak to me ,but i'm just not sure anymore. the needles are set in the middle notch and thier is no dirt anywhere in the carbs.............help..........thanks

I think that the bike needs to be adjusted for how "free flowing" the air intake and exhaust are.  If you're putting your hand over the carb air intake, then you have no air filter or airbox on.  Even if you get it running perfectly, it will probably not run well as soon as you add the airbox.