| first thing first ya will have to work out if its leaning out or flooding & stalling out from 2 much fuel ? (drowning the spark)
another thing to try would be to throw the filter on & choke it a touch, see if it makes any difference
it could be somthing to do with air velocity going past the venturi & large droplets forming or the oppisite & not getting enough flow to draw the fuel up the main jet ?
was it fine before with the reed setup & different carb ?
try the old carb again & make sure its running good & to confirm its the carb or you will end up chasing your tail all day long | 
