I'm having quite a fun time trying to get a project up and running. Any idea how critical exact compression numbers are for running. My manual shows 2 number first the decompression affected and second with it not effected. Shows 78-120psi and 171-201psi. I've got 90 and loosened exhaust valve and had 150. My first reading is technically within spec but the second is low. Getting spark and fuel no kaboom at all though. Those numbers seem low enough to cause the bike to not even start?
bike Is a foreman 400

 

Yellow spark is a weak spark, it should be blue in color to be a good hot spark. Is plug wet with fuel after a start attempt ?? Fouled plug?

 

Kymco, nice blue spark. Brand new oem coil, cdi and plug. Its wet with fuel, although after cranking for awhile the plug will soot up. Comes off with just a paper towel but very dark. Even if I shoot some ether in the carb I may get a slight sound like it wants to run and then a backfire out of the carb.

 

My guess at this point is it is getting flooded with fuel or the timing is way off. Bring piston to tdc and check timming mark. After that it is getting to deep for my expertise. There are ways to check the new electrical components you have to be sure they are good, perhaps someone else might jump in here with knowledge of testing those parts. Even beans new parts can be bad from the start.