single fire ignition? or something is f'd up

[dirt_humper88]

i just put a big bore on my 400ex, now it wont start, sounds like it may be sparking on TDC Overlap and not TDCC, is this the problem?

[Honda5]

it fires on both strokes so that can't be the problem re check your timing marks and make sure the flywheel didn't shear the key.