Sir,
This is the reason I advocate to anyone building their first performance engine that unless they have prior experience and can expect the results of any given modification, that they start by doing one mod at a time.
Your engine is loaded down with mods and aftermarket accessories. It is extremely difficult to pinpoint where you problem might be. A better alternative would have been to start with the porting mods, tune for them then move to the piston and so on. That way you would have known what worked and what was causing a problem. As it is we can only guess. An option, that you probably don't want to hear, is to replace those go-fast parts with stock items. I'd start with the CDI. If that doesn't cure your problem then move to the carburetor, and so on. That at least might help locate a troublesome part.
You say the engine "sputters" but doesn't start. Does this mean it is firing but won't continue to run, or, is all you're hearing compression sounds when you pedal? Define "sputter" for us.
Have you been through the common checks for an engine that doesn't start?
Checked for ignition (plug sparking)
Checked for good fuel flow to the carburetor from the tank?
Checked to see that the choke is open (if equipped)
How is the compression?
Tom
