i just decided to put a 250r engine in my 400ex. a have a 250r(88yr) motor on the way. has abyone else done this if so any tips. and its comes with a 39 kiehin carb. and suggestion on jetting(main, piolet, needle) i also hase aftermarket pipe. thanks hopefully it will run in a month at the most

 

does the motor have work done to it?
if yes then use that carb if not its to big
it better have a good pipe. will the pipe fit without modifing it for the frame
you should have plenty of room.
your 88 trx probably has better geometry then your
ex but go for it
the allen knowles from ct racing would probably be the guy you want to hook up with he started that revolution of motor swapin.

 

yeah it has a 310 kit in it. and i don't have a 250 frame i just bought the motor and sold my 400ex motor. it has a lrd aftermarket pipe and will there be enough room for the pipe