In need of help bad.

[Silver400EXinBR]

Ok, i got a 2001 400ex. I bought it and it had a uni air filter and fully yoshimura exaught headers and pipe. He paid like 700 some dollars from it. It has a 155 jet in it. ANd it seemed like it slowed it down. I raced a completely stock 400ex with a procircuit t-4 pipe and lost by like 4 bikes. People said that the headers was hurting it due to not having anything done to the motor or anything. So this morning I put stock headers on and a friends supertrap pipe on that and it still feels the same and it like pops now when letting of the exaust when in neutral and when riding.. it rides good when giving gas just giving off it pops. but it doesnt have any plted in the pipe rioght now either. But with that exaust set up it feels the same as with the headers and yoshi.. What can I do to get better performance out of my bike?????

[Atreyu]

Your jetting is lean. You'll need to go to your local shop and pic up the recomended main jet. It's only around $3.

[Toadz400]

The problem is your jetting. What's the temperature and altitude? Also what is your pilot jet and needle set at? A guy that lives by me had the same problem with his 406ex with a full Big Gun exhaust, everytime he let off the gas it'd pop pretty bad.

[nikejoe]

So is there any consistency (sp?) to what you are saying about the jetting? What I'm asking is if they pop are they too lean? or too rich? or can you not tell by that. Mine pops quite a bit! But according to the plug test a 155 main is what I need. Plus it sounds COOL! But if that means it's too lean or rich, I will obviously change it???? Any thoughts????:p

[300exOH]

If your exhaust is popping then you either have an exhaust leak or your jetting is lean. Are you doing a plug test for all carb circuits? You may be correct on the main jet but lean on the pilot. Also check that the fuel/air screw is set correctly. (Not sure of exact setting) Try a search there are a few very good posts on how to set the fuel/air screw and pilot settings. There are also some good threads on how to do a plug test to make sure your jetting is on. Good luck.

[cals400ex]

i would think a 155 keihin would be in the ball park. the race doesn't mean too much without knowing more variables. you have stock gearing? you have stock tires? are you using keihin or dynojets? is your throttle cable ajusted properly? are you both equivalent riders? switch bikes and see if you get the same results.