I'm gonna hazzard a guess (but I wish greg were here)...
It really sounds like a carb issue, maybe the spring for the slide is out of place or you routed one of hoses to the carb incorrectly.
check your air filter (ok now where are those straws)
all the plumbing to the air box.
if all else fails, check the valve timing. I think the intake should close before tdc and the exhaust open after, with a full rev inbetween. Anybody know exactly?
did you check the vac line for fuel?
are you running on prime?
That's it, out of straws, good luck.