...its possible to have a weak spark if the wiring is wrong, but than, which i have done, blew up my CDI...so check your wiring...to be safe only hook up the ebgine to the CDI wires...no white...blk to blk abd blue to blue...check your spark plug gap and if its foiled out replace it...sounds like your getting gas...so get on the wiring...leave the kill switch off for now...do you have a integrated kill switch...small soiderd wires in there can come loose...do that for now...process of illimination...you'll get it...than i'll tell you a few more things...just make sure all the bolts are snug...incase this takes off...ha...go getem...talk at you later...
Excellent advice from an experienced MB'er!

I will add:

1) The factory bullet connectors between the engine and CDI are really crappy...make sure that they are tight by crimping the female end lightly with a needle nose plier.

2) When these engines are new you really need to get peddaling at a good clip before releasing the clutch.

I have had several customers at the shop that would release the clutch too early, and the engine would pop over a few turns before the rider came to a stop.

Pedal it up vigorously...release the clutch...and keep peddaling so that the engine continues to turn over.

Crack the throttle as you are peddaling, then return to idle, crack it open again...listen for the engine to sound like it wants to start...then crack the throttle back to that point that made the engine pop pop.

Once it is running, (and you no longer need to pedal), go easy on the throttle...You don't want to push it early on.