I'm new to this, so please bear with me. I just rebuilt the top end in my 88 250x it has 160 lbs. compression and good spark but it still won't even pop even with ether. I was wondering what else it could be. The timing is set right, valves down at tdc with the cam sprocket marks lining up with the head. I looked at the flywheel and everything is in good condition... now i am completely baffled. Thank you in advance for any advice!