I cant get my 400 ex to start after i just did a complete top end rebuild and split the case of the motor to get the chunks of piston out that the previous owner blew up. Here is what i have done so far and any help would be greatly appreciated to get this thing running!

1.Split cases and flushed everything out and reassembled.
2.Reassembled top end with used jug and piston that was bought used but in good condition
3.put cylinder on and rotated motor counterclockwise using the crank bolt until the piston was at TDC
4.put the head on the cylinder and never moved the piston postion
5.put the cam sproket in the timing chain and made sure the two markings were lined up horizontally with respect to the motor and the one mark vertically.
6.Put the cam in with the lobes facing downward to set this as what i think is the compression stroke.
7.put the valve cover on and adjusted the valves to .005 on the exhaust and .004 on the intake. I did all of the last 4 steps were done without moving the piston to make sure it stayed at TDC.
8.Tryed to start the engine and im getting nothing. It is turning over and only backfiring every once and a while (no apparent pattern or common occurance) but it is backfiring through the carburetor??
9. i know it is getting gas because the plug will be wet when i pull it out. I have tried new plugs also
10. i have spark when it is grounded against the motor it is nice and blue.

I did notice when i was inside the valve cover tonight, that if i took my finger and put it over the decompression plunger, and pressed it in while sliping my finger off the hole of the plunger, i could here air releasing. In other words, with my finger over top of the hole in the plunger, it was compressing air as i pressed the plunger into the head?? That may be the correct thing for it to do but im just trying to give you all the information.

any help is greatly appreciated as i have been at this thing for 3 weeks now with nothing!!

 

Have you verified you have the correct amount of compression?

 

Did you check the valves had not been bent during the "blow up"? Also check that valve timing again. There should be a TDC mark on the cam and the flywheel.

 

I have not checked the actual compression number but I will. Should I do a test with the valve cover off so that all the valves are "closed"? And the head I bought was also a used head I forgot to mention that. All the valves looked to be seating properly as well

 

May do an leakdown test to see if top end is leaking down and where at.....Also did you preload cam chain tensioner ?