New motor....clunk, clank, blah blah blah...

[flootiebuell]

So plug out turn motor and there is resistance at top dead center. Pulled crank gear and still have resistance at TDC. Normal on Chinese motors? Any ideas? Oh and won't start...new motor, spark, gas, blah blah blah. Noticed the loud clunk the first time I tried to pedal start it. Pulled the head, clunk went away....put head back on...no more clunk! Still no start...got spark albeit a bit sporadic...popped a couple of times.

 

[crassius]

clunk may have been a head gasket really crooked that got straight after removal

CDI may be making weak spark or motor just isn't turning fast enough - I've seem single speed bikes that are so hard to pedal that starting is real work

any chance you know someone that will let you try their CDI?

 

[Davezilla]

Almost sounds like the piston was hitting the head but removing the head and reinstalling it made the clunk go away makes me think maybe it was hitting the head gasket. Did you check the head gasket for any signs of the piston hitting? It's possible that the piston hit the gasket the first time around then left it distorted enough to leak preventing it from starting.
Chances are that the cdi is bad too since there was a bad batch sent out about a month ago so there's a strong chance it's a bad cdi if the head gasket is perfectly flat and ok. Another issue with these is that the acorn nuts can tighten down but bottom out on themselves making you think the head is torqued down properly when it's not. Getting a set of regular nuts from a hardware store will fix this problem, you can also use 2 or 3 washers under each nut if you can't get the standard nuts to keep them from bottoming out on themselves.
Other things that'll prevent a start are leaking base gasket, leaking intake gasket or a leak at the carb to intake connection from the carb not being fully seated. The case gasket can also leak at the split line but this is more unlikely, it can happen tho if they were in too much of a hurry assembling the engine at the factory so worth checking if everything else looks ok.
The most likely cause is either the cdi being defective or the head gasket damaged or the acorn nuts bottoming out before the head is torqued down enough to fully seal.