I just rebuilt my 400 to a 416. All I added was an 11:1 JE piston and a TC Racing cam. I put it together and after putting everything together properly, it ran perfect. I was so happy that it was finally running. It ran awesome too. I took it for a little ride, trying to vary throttle and not hold it wide open. I let it sit a few days then it wouldn't run. I don't know what happened, but now it seems to suck in through the exaust. I thought it might have jumped the timing, but it didn't. It doesn't have compression anymore either. There isn't a whole in the piston either. The only thing I haven't checked is the rings, but if the rings were gone, (which they shouldn't be) then it wouldn't have compression, but wouldn't suck through the exaust, would it? It has spark and gas too. Please help.

 

It sounds as if you have valve trouble. Either a broken valve or bend one. I would check the whole valve train, valves, springs and rocker arms. Anyway, good luck!

 

This happened to me almost exactly as you stated. I took it to the honda shop expecting them to tell me I blew the engine. They said I sheared the key on the fly wheel, They fixed it and charged me $55.00. I was a happy camper.

 

Thanks for the help. I'll double check the head again, and I'll check the flywheel key. I hope that's it but I won't get a chance to take it apart until Saturday. I'm starting to get frustrated with it. I hope I'll find something though. Thanks again.