hey, i got a new carb for my ryobi (ditched the single needle one) and now it wont draw fuel when i try to prime the engine (i put my finger over the carb and flip the prop). i think ive got the fuel line hooked up on the right nipple, but htis carb is a tad bit different than my other one. it has a small brass nipple beside the needles, and a large plastic one on the other side of the carb. i have tried both, and still havent got this to work. the carb has just been rebuilt ( the guy i bought it from rebuilt it right in front of me). could there be a leak at the manifold? or is there another problem?