is my jet too big?

[Bush0102]

i have an hmf slip on and a k&n airfilter, and i dont run an airbox lid. The jet i was supplied with was a 170 mainjet...is that too big? am i going to have problems at higher elevation?

[redlined94]

You should be alright. In fact I just bought a 180 main jet for mine because it hasnt been jetted and I am running a full HMF system, no box lid and and aftermarket filter. As long as you arent fouling out plugs due to too much fuel and not cutting out and backfiring due to not enough fuel then you should be good with that 170

[cals400ex]

i indeed say its too big. others will disagree. go smaller and you will gain some more power up top.

[redlined94]

I am gonna have to disagree. With all that stuff you gotta get more gas in there to mix with all the new airflow. Its pointless to have all that if you wanna have such a small jet. Just go back stock if you wanna run such a small jet.

[hondarider2006]

Originally posted by redlined94
I am gonna have to disagree. With all that stuff you gotta get more gas in there to mix with all the new airflow. Its pointless to have all that if you wanna have such a small jet. Just go back stock if you wanna run such a small jet.

I will have to agree with Cal. He is the jetting expert on the site...so I would say listen to him. Yes you have to re-jet when adding more flow, BUT there is a limit. Once you pass that you will just start loosing power. Do a plug test, my guess with nothing but a slip-on and an open airbox lid a 170 is way to rich. I run a 175 and that is with a lot more done to my motor than what he is saying. Go down to a 160 and do a plug test. I bet you will feel more power;)

[mojoe2878]

a 170 is huge with what you say you have one there. i wouldnt run a 170 unless you had the cylinder board out some to need that much fuel.with what you said you have i would try a 160 or 162 keihn. if you use a dyno jet kit then something a little smaller because the dyno jet kits have a higher flow rate than the keihn. a 160 dyno jet would be like runnin a 165 kehin jet or somewhere around there.

[cals400ex]

i run a keihin 158 in my 11:1 426. air box lid is on and i am at 625 feet. as you get more motor, you will get more vacuum. this will enable you to pull more gas through the same jet. my jetting changed one size from stock bore to a 10.8:1 406 with stage 2 hotcam.


i realize some people won't agree with me, and that is fine. i have 19 mainjets sitting in my jetting box and believe you me i have tried plenty of different setups. i don't have my bike totally tuned in now after i put on the ported head. it looks like my jetting got a bit richer after the ported head. however, i have been told this may be the case.