My bro in law just put a pipe on his 99 400 EX , sorry I do not know what kind it is but
he put a 152 jet in and it will not idle and when he revs it back fires.
He needs info on the 2 spacers where the jet screws in to or is there any other info we can get
we are leaving for Dumont tomorrow and he will most likely be messing with this all night

Thanks so much in advance

 

try putting another size jet

 

Is it the main jet that could be causing this or pilot and air screw adjust. ?

 

Sounds like you need a 40 or 42 pilot jet and about a 155 main jet. Pilot adjust would also be nesescary. Try putting the choke on a little and see if it clears up a little, and that tells you that you are getting too much air and not enough fuel-AKA lean.

 

Look at the intake manifold. If its still the original, it could have cracks in it. Did you replace the headpipe? If you did, did you replace the exhaust gaskets? If the gaskets are not replaced, its harder to get a seal. I screwed up my stud bolts at glamis trying to get them to seal. These simple things have been a burden for our rides. I just had to put a new manifold on my 99 and so have many of my friends.