Never used a forum so this is new to me but hopefully someone has some good input because I’ve never been stumped this bad. Just rebuilt my 2003 Honda 400ex with a 440 big bore kit and hot rods crank. New valves and seals which were lapped and readjusted to spec. getting spark,fuel,and compression is at 110-115psi, which to me seems a little low.bike will not start only backfires occasionally. Checked timing over and over and it is correct.timing chain was stretched and really loose when I got the bike but I put a manual tensioner on and it’s tight again. piston is highest at tdc so I don’t think the flywheel key sheared.it’s the stock cam, the plunger and spring were missing and I put them back in ,still nothing.looks like someone before me cut the longer tab off of the rocker that controls the decompressor but from what I could tell that only affects the reverse decompressor.I’m at a loss and really don’t wanna sell it.Any input would be appreciated, thanks.