lost and need suggestions

[soonerdude77]

Sorry for having to ask questions on the first post, and it being somewhat lengthy but I'm trying to give all the details so maybe someone can help me.

I'm in the process of buying a "project" '00 400EX from a friend of mine but we can't get it started. The confusing part is that I was there when he rode it into his garage and we tore the top end down. We knew it had some piston/cylinder damage to begin with due the clouds of smoke and oil being puked out through the exhaust but after looking at the piston it defied all logic by running in the first place much less not being locked up(cracked skirt, oil rings glazed over with aluminum, etc.) So we got a mild bore(402), new piston, gaskets and went back to a stock cam since the WB one that was in it was toast. We didn't want to trust ourselves with putting it all back together so we had someone who knows what he's doing put it together for us.

Now when we try to start it, the motor turns over and thumps but it just won't fire up and run. We've checked for spark, checked the timing, tried spraying gas/ether in the carb, checked the valves, and cleaned the carb, but we can't get anything more than the thumps. The only thing we changed with the rebuild that I can see causing the problem would be going to the milder cam but I don't know why that would cause a problem. Any suggestions?

[fastredrider44]

Maybe check timing and valve clearance again. If its getting spark, getting gas, and has compression, it has to be something to do with the timing.:devil:

[rideracelivemx7]

do you have spark? if you have spark and have fuel it should start. in this case its a 4 stroke. your buddy might have put in the cam in the wrong position. back wards 180°. causing it to still open teh valves but not at the right time and on the wrong stroke.

[fastredrider44]

I was being a smart aleck. I'm the one who is selling the fourwheeler to him. We had one of my friends do the assembling. It's definately not 180 out. The problem is that it has a shaved flywheel, and that's making timing difficult because the t mark is nearly non-existent. Didn't know if anyone else might have any suggestions. It fires every cycle, just won't start. We're losing our patience on it, so we're taking it back to the guy that put the motor together to see if we can get it figured out. Also afraid that the rocker arms might be wore out to the point that it's not opening the valves far enough or something. Its wierd that when you try to give it a little gas, it quits trying to fire.