Serious jetting question Please Read

[400EXSTUDMUFFIN]

I have an 01 400ex with a FULL R4 exhaust and a K&N filter with outerwears. I was told by White Brothers that the R4 pipe was made so you dont have to jet your carb. The bike runs good now I just want to know if i jet it will i get any more power. And what jets do you think would be good for this set up.

Also will the choke delete and 42 pilot jet help this set up as well?

[jshtex]

If it was me, I would at the least go buy one keihn jet that is bigger and try it. Changing the main jet is fairly easy, with the carb still on the quad and the jet should be cheap. If it is running a little lean now it will rev great but it will not pull as hard as it could. So if you go up a few sizes and it pulls harder you will have an answer. And it is always better to be too rich, then too lean. Maybe try a 152 or 155. In the old days you could "read" a plug and see if it is lean or rich, but from what I understand the detergent in gas now makes this more dificult.

As for the choke, we pulled ours off, but we did it at the same time as some other things so I can't really say. We are in Texas so cold starting is not an issue.

[2004TRX450R]

Originally posted by jshtex
In the old days you could "read" a plug and see if it is lean or rich, but from what I understand the detergent in gas now makes this more dificult.

You can still read the plugs just fine if you now how to read them.

[400EXSTUDMUFFIN]

I have a full dyno jet kit! I just have not used it because I was told by WB that I would not need it. I live live in florida so there wont be a starting issue here either. I will ride the bike tonight and see what the plug says but I think i do want to go up a jet just to see what happens.

[jshtex]

2004TRX450R... I didn't say it was not possible, just that it is harder (if you are running pump gas, which I assume he is). If you type in "plug reading" in the little search box below you will see what I am talking about. But over and above this site, both the guy that dynoed my 416ex and the guy that ported the head said the same thing.

[400EXSTUDMUFFIN]

Well then not worring about plug reading what does eveyone think about the jettting?

Should I give it more jet or stay here?

If so what size jets to put in it?

[BBW]

If you search on jetting you will probably get about 10,000 hits and as many opinions, many of which are right.
One thing for sure, you do not want to run to lean. My son and I (until this last week-end) both had identical set-ups, WB E series, K&N filter, 155 main. I could consistently beat him by a length which we attributed to him having 40 lbs on me. Last week we decided we were going to try running without the airbox lid to see if there was much of a difference. Through a racing friend of his he opted to change to a 172 main and I went to a 165 as I was certain the 172 would be too much. Needless to say I was a bit surprised when he left me in a wake of sand. Am I going to go to a 172… I’m going to try it but depending on the outcome I may go back to the 155. Even though our machines are identical right down to the hours they aren’t the same and what works the best for one machine may not work for the other. Jetting, at least the main, is something that for $20 bucks you can get a whole variety and find what works best for you with little trouble.
Good luck in your quest for the, “right” jet which you may already have.

[400EXSTUDMUFFIN]

Thanks alot for the info. I will be in search for the correct jet ASAP.

I think I am goin to go up a too a 155 and see what happens if that is good then i will try a low 160jet and also change to a 42 pilot jet with no choke

[cals400ex]

hold on a second. you said you have a jet kit. this comes with dynojets. our stock carb is a keihin carb. so, a 155 dynojet is NOT a 155 keihin. yes, if you went and bought a 155 keihin, you should be in the ball park. however, a 155 dynojet is probally too big. i would probally start off with the 146 dynojet. i haven't used dynojets before, but from what i read a 146 seems like a good jet to start with. good luck

[livealatimmy]

I agree with the above post. when i had a HMF slip on and a k&n filter w/ outerware i used the 146 Dynojet and it seemed to be just right. But jetting is a trail and error type of thing. Have fun:D