jetting question

[markvette]

we just go the motor back together on our mx 400 ex. it has a sparks built 440 motor on it with a 39mm fcr carb. we have broke the motor in and tried a couple half to 3 quarter throttle runs. it seems to miss or sputter a little in fourth gear. the only changes made since we put the motor together is a filter change. the quad had a nasty looking k&n on it when we bought it and i put a new uni filte on it. do you think i may have to rejet the carb for the different filter. it has a 155 in it and i have a 165 and a 175 to try in it

ya u will prolly need to rejet

I dont have the fcr but from what I allways hear they like bigger jets than what you would run in the stk carb.

Try the largest you have and do a main jet run and see what you find and go from there.

[markvette]

when my son gets home today we will put the 175 in and make a jet run with it. another thing i thought about. i bought a uni for both my sons race quads one rides a highly modded e-ton 90 and then the ex. the guy i got the one from for the e-ton told me to only oil the inner filter and not the outer. it will not run with the uni till i get some bigger jets. all it does is bog so i had to put the stock filter back on it. i wonder if i should try oiling the outer filte on the ex first before i try jet changes. what do you that run the uni filter do, oil both or just the inner ?