problem starting 400ex after rebuild

[03'400exrider]

Another problem of mine on a different 400ex..
i have put a new cylinder, piston, and cam in this bike. After the rebuild, the bike will not start. It hits once, then turns over twice-- then repeats very consistantly. I know the valves are good and not bent. I also believe that the timing is correct because it is set EXACTLY like my other 400ex that runs perfect. The bike ran before rebuild, but the piston was bad. Does anyone know what might be the problem.

also, after rebuild the compression reads to be 115 psi

[f4istunna]

115 is low. Are you sure you have the rings in the right position on piston?

[drew416ex]

that psi would be good on a stock setup. Did you make sure the valves are adjusted right? A lot of people dont adjust the valves after putting it back together causing it not to start because they are staying open too far.

[03'400exrider]

valves are set correctly...i think i know what the problem is though...i found a little piece that looks like a roll pin on the floor after rebuild. After investigation, I believe that piece is the cam plunger...which may be my problem....

does anyone know exactly what the cam plunger does?

[f4istunna]

you need it if using stock cam w/ decompression assembly on it.

It goes in the head w/ a spring under it. Spring might still be in the head, just put the pin in and see.