odd problem, need help

[rubbersdown]

My bro in law has a 99 400ex. He just did the rings on it and its running very odd so he dropped it off to me and said "fix it" lol.
It starts up just fine but tics kind of loud and the throttle has a really hard "thump" in it when the bike is running, almost like its pushing back and resisting. When the bikes off the throttle feels normal but when running it feels like something is hitting the carb or something, its a pretty hard thump. I have never personally felt this before. Anyone have any ideas? My first guess is that maybe he put the cam in 180* out and its backfiring out the carb and thats why I can feel it in the throttle? Although it seems that if the carb was out 180 that it wouldnt start?

[rubbersdown]

well I just talked to him and he said he "thinks" he put the cam in lobes down lol. still going to check anyway but any other ideas? Could it do that if he put the piston in backwards?

[fast2007]

If pistons in backwards it could hit the valves and if he changed the cam make sure he bolted the cam sprocket on the right side of the lobe..It will go either way..

[killer454]

make sure you put lock-thread on the bolts for the cam gear,they could fallout later causeing major damage.

mine was backfireing or poping back through the carb and it turned out to be the intake between the carb and head come apart,look for leaks in this area.

[rubbersdown]

huh, well I guess im just going to have to take it apart and see what the hell he did lol.