Main Jet

[cmw680]

Would anyone here happen to know the size of the stock main jet.....I am going to be installing an aftermarket pipe...


Is it a must that I rejet if i install a new pipe.

Thanks,
Chad

[jmoney45]

I think stock main is a 145. You are going to have to rejet with a new pipe, as you will have more air moving through your motor. If you don't rejet you will be lean. Are you doing any airbox/filter mods as well? I would start with the recommendations from the pipe manufacturer and go from there. Just look at your plug to determine if you are too rich/lean. You may want to consider a bigger pilot jet to help with starting also. I run a 40, but a lot of people run a 42 (stock is 38). Good luck.

[White_Knuckles]

You need to provide the pipe make/model, airbox mods including filter, approx. altitude and if your engine has been built up like cam or bore increase.

Then we can give you a guess but the research and field testing is up to you.

[Colby@C&DRacing]

It looks like you have a 300ex. If so the stock main jet was either A 128 or 132 depending on the 300 some had one or the other.

[cmw680]

Thanks for all of your help....guess I'll just pull the carb apart and see what it is.

Chad

[jmoney45]

Originally posted by Colby@C&DRacing
It looks like you have a 300ex. If so the stock main jet was either A 128 or 132 depending on the 300 some had one or the other.

Ooopps. Good call. I assumed he had a 400. :uhoh:

[DirtDiggler]

I thought stock for a 400 was a 148? Is it a 145?

[TravEX]

yes 400EX is 148.

[toby400ex]

I think the 300ex stock main is a 122