carb jetting

[linkindust313]

heyhopefully someone on here can help me out.....last winter i had a hot cams racing cam put in my 400ex and also had it ported and polished..it seems like it isnt running like it should...i am getting passed on a straight away by stock 400's .....should i change the jetting in order to gain more fuel flow since it was ported and polished? it is already jetted but im not sure what jet is in it...i have a yoshimura exhaust and k&n filter also...and ideas to gain more power would be greatly appreciated...thanks
John

[zephead400ex]

Do you have the stock jetting in place? Where are you located?

[linkindust313]

im not sure.....the guy i bought it off of had a pipe on it and he had the filter and jet kit in place...im guessing he actually changed the jets...im not sure what number the main jet is tho...i am from latrobe pennsylvania

[MichaelS693]

check your spark plug to see what color it is and get ahold of me in the morning:D

[Shocka400ex]

I have a question about the jetting in my 400ex.
I purchased a dyno jet kit a while ago and put in a 42 pilot jet and a 146 main jet. I really didn't see any difference from stock, so I decided to remove my air box lid and put in a 170 main jet as the directions told. My motor now seems like it's bodged down. I am In Phenix AZ and the elevation here is under 3,000 Ft. Can Anyone give any advise so that I can get the most response out of my motor.

[cals400ex]

Originally posted by Shocka400ex
I have a question about the jetting in my 400ex.
I purchased a dyno jet kit a while ago and put in a 42 pilot jet and a 146 main jet. I really didn't see any difference from stock, so I decided to remove my air box lid and put in a 170 main jet as the directions told. My motor now seems like it's bodged down. I am In Phenix AZ and the elevation here is under 3,000 Ft. Can Anyone give any advise so that I can get the most response out of my motor.


i bet your motor did bog down. i would try the 155 or 160. your jetting is too rich. by the way, you probally won't notice any difference in power from the dynojets to the keihin jets. the key to which ever one you use is getting it dialed in correctly. i prefer keihins jets because that is what i started with and i know the increments better. by the way, you will always hear a bogging sound when the lid is off because of the noise and vibration you feel on the seet.

[cals400ex]

Originally posted by linkindust313
heyhopefully someone on here can help me out.....last winter i had a hot cams racing cam put in my 400ex and also had it ported and polished..it seems like it isnt running like it should...i am getting passed on a straight away by stock 400's .....should i change the jetting in order to gain more fuel flow since it was ported and polished? it is already jetted but im not sure what jet is in it...i have a yoshimura exhaust and k&n filter also...and ideas to gain more power would be greatly appreciated...thanks
John


first, make sure your throttle cable is adjusted properly. you need about 1/8 inch of slack in the lever. if there is more, adjust it. this will hurt your performance a large amount if it isn't right.

second, you need to dig in that carb and see what jets are in there. we need to know if you are using dynojets (jet kit) or keihin jets. there is a difference in the 2 types of jets. your jetting is another thing that will kill your performance if it isn't right.


it would be hard to tell you what jets to run without knowing your elevation and temperature and the brand of jets being used.

[Shocka400ex]

Thanks Cal for the info. I think the best bet is for me to put a 155 and try it but I think I'll test a 160 too to see which one dials in the best.

[cals400ex]

Originally posted by Shocka400ex
Thanks Cal for the info. I think the best bet is for me to put a 155 and try it but I think I'll test a 160 too to see which one dials in the best.


sounds good. i would probally go smaller than a 160 if i had to guess.