Need help please !! Picked up a 660 with alot of mods , but not running , would turn over real easy like out of time , pulled top end found bent valve , replaced all valves, springs, guides , cam chain, tensioner , heads in great shape ( stage 2 hot cam , new weisco crank and all seals done by previous owner ) installed new 686 big bore kit , now having an issue where it turns over and pops once then like no compression, ive pulled cam and reset like 5 times marks look perfect , im lost please help guys TIA..

 

Wonder if one of the guides is a bit tight and a valve sticking open, worth checking clearances when the fault is on, if one clearance has increased a lot, that valve is slightly open.