rebuilt 400ex won't start.... NEED HELP BADLY!!!!!

[nuckinfuts]

Yes if the valves are slightly open then your pressure would suck. However it probably wouldn't start at all if one or both valves were overtightened cause it would be blowing the intake air/fuel mix right back out into the intake, causing backfire as soon as it sparks. Sounds like you have it figured out. Keep your battery at full charge or you may run into some impossible starting.

[JeffinTD]

<div class="FTQUOTE"><begin quote>I was getting about 6-7:1</end quote></div>

What he's saying is the compression gauge should give you a pressure reading, in PSI.

If it doesn't continue to backfire, you might run it for a while and see how the plug looks...

[dufrenbk]

Yeh, I read online and it said for the pressure I was getting that it is about the ratio I stated. I seriously don't think this monster's lacking compression though [img]i/expressions/face-icon-small-smile.gif[/img]

I'm going riding this weekend and it will definitely get its break-in period or whatever it should be called [img]i/expressions/face-icon-small-smile.gif[/img].... if it doesn't just.... break =P

[JeffinTD]

I think it's compression ratio is like 9:1. Book says 100-128 psi is normal.

Anyway, have a fun ride.

[dufrenbk]

Well, I really got to test the 400ex out this weekend. We went about 40 miles on some trails, some pretty rough stuff, and I drove it pretty hard and it's still going so...
I guess it's all good. It WILL NOT start from cold on a low battery though, which I seem to think is normal, and I am thinking more and more that I probably have an after market ignition. I brought my charger and had jumper cables just in case though. Just wanted to leave an update on the quad and tell you all thanks again for the help and concern! Excellent forum!

[nuckinfuts]

Thanks for letting us know! Forums are nothing without willing people and riders! Have fun and post some pics up!