ive had the idea to do it to mine get a mini 90 from raceway atv then go on ebay and search xr50 and buy one of the 125cc manual 4sp motors being as they have the same motor mounts only real modification needed is diffrent foot pegs welded on in order to reach the gearshift and also get a xr50 performance exhaust will hook up with motor and since most of them use a hanger that goes around the whole pipe there no fixed mount on the pipe so as long as the silencer fits under the rear fender which it will it will be able to be mounted ive heard 90cc production 4strokes are allowed to run a 125cc thats where i got the idea and the cool thing is now this little quad has a clutch and 4spd tranny i figure if a kid wants to get into racing heres a cheap way

 

Most quad racing associations require that the motor be from a quad, unless you run it in the class with the 90 mods.

 

It sounds good. But that mini would not be allowed to run in a AMA 90cc Production race. You would have to run it in the 90 mod class like nenkick said.