jetting

[linkindust313]

hey I wrote a thread before saying that i have a ported and polished engine with a k&n filter and Yosh pipe. i looked at my carb this weekend and i have a 38 pilot and a 146 main in it. My elevation is about 1200 ft. does this sound about right?

[cals400ex]

Originally posted by linkindust313
hey I wrote a thread before saying that i have a ported and polished engine with a k&n filter and Yosh pipe. i looked at my carb this weekend and i have a 38 pilot and a 146 main in it. My elevation is about 1200 ft. does this sound about right?


i would go up on the pilot jet for sure. a 40 or 42 seem seem to work pretty good. however, on a built motor with an open airbox lid, a 42 or 45 are usually used. is the jet a dynojet instead of a keihin jet?? the stock size mainjet is 148 but the numbering technique is different between the two brands. so a 148 keihin is NOT the same as a 148 dynojet. if it is a dynojet, that may be about the right size. i know rico on here runs that same jet in his motor and i think he even has some work done. i would make sure your just not too lean from 3/4 to full throttle. if thats the case, you need to go up on the main jet a size or two.

[linkindust313]

alright thanx for the info. I think they are probably dynojets, the guy that had the quad before me bought the jet kit when he got the k&n filter. The quad runs good now, but i was thinkin maybe if i change the jetting it will give a little more pep...idk...I have this motor work done (port and polish and cam) and i am getting passed by stock 400's. I dont know what else would be slowing it down...i also just bought a sparks advanced ignition key can you feel a difference with those keys?

[cals400ex]

if the kid gave you the jet kit with the bike you could try going up one size. i do recommend not going up more than one size though.

here are a few things to check as to why your getting beat:

1. make sure your throttle cable is adjusted properly. if you have a lot of slack in the throttle lever, its not adjusted right. you adjust this right up on the handlebars. adjust it so there is less than 1/4 of an inch of play in it. this makes a pretty big difference in a race.

2. if your running aftermarket tires, they can slow you down. if they are aftermarket, what tires are they and what size are they?

3. running different gearing can hurt you in a race. did you change either one of your sprockets?

4. when putting the mainjet in the bike, you could have messed with the correct position on the needle jet holder. this is the piece that holds the mainjet in place. you will notice there is a nut on this piece. when you tighten the nut down, you should be able to see 3 to 4 threads on the needle jet holder. if you can't see that many threads, back it out some and tighten the nut down. this also harms your performance especially in the upper gears.

[linkindust313]

alright thanx man....u still think i should go up on the pilot jet too?

[cals400ex]

Originally posted by linkindust313
alright thanx man....u still think i should go up on the pilot jet too?

i would go up on the pilot jet and then tinker with the fuel skrew.