my brother bought my nephew an 03 80 raptor for Christmas. i tore it apart and repainted all the frame and such and was gonna do a tune up on it. the local yamaha store gave me the wrong spark plug for it...needless to say i didnt pay any attention to it being the wrong one and put it in it. lesson learned because it was too long and caused the valves to beat the plug. so at 1 in the morn Christmas morning I tore the head off of the motor to see why it wouldnt fire, and found that both valves were dinged up and would not seat. so i had to have to new valves and seals put in it for him. now it starts and runs great, except it has throttle surges. it will rev up on its own...if you hit the throttle and rev it up, it will go back down to idle. but this just isnt safe for him to ride with it doing this without me or my bro riding on the back with him. what is causing this? and what do i need to do to fix it?

thanks in advance

 

have you checked the needle in the carb to make sure it's operating smoothly?

 

it was tore apart, soaked and cleaned. needle was replaced and the seat is built in the carb and i took a cuetip and brasso and polished the seat. but if you think this is the problem, ill tear it apart and make sure its good and clean again. the carb was terribly gummed up when i tore it apart where it had set for quite a while before i picked it up for him. also i did notice when i went to make sure the valves were set right, the exhaust valve adjustment cover had a little oil in it. wasnt sure if this was normal for a horizontal motor where that its on the bottom or not. if this isnt, could this be part of the problem and what needs to be done about it?

 

It could have an air leak. Spray WD40 or carb cleaner on mating surfaces one at a time. If rpms quickly drop or raise then there's an air leak there. Use caution when using WD40 or carb cleaner on a hot engine.
Also check the intake boot for any cuts and check to see if it's loose.

 

I agree. You have an air leak somewhere