Jetting help for ehs airbox lid

[erik420]

Hello everyone. I have a stock motor 400 ex with a slip on, uni filter and ehs lid. I just added the lid and now I have a pop or backfire now when it is warming up from dead cold... One warm it will do it one or so an hour when ridding. Jetting is 38 pilot and 155 main. All keihin jets. Ran fine prior to adding the lid. Has a fresh carb cleaning and gas with a new plug and filter. Im I running lean now with just adding an open style lid? All the adjustment screws on the carb are at factory setting. Would adjusting the air fuel screw help? If so what whay do I turn it? Any help would be great. Oh and im about at sea level.

Sorry for the long post. Lol

Thanks,

Erik

[TheAwesomehonda]

You need a 42 pilot jet and maybe a like 165 main jet. 2 1/2 turns out from seated on the a/f screw.

[Drfat400ex]

Lol 165 is a little high, I only had to bump up one jet size when I added my powerlid, I'd try a 160 and a 158. I would also get a 42 pilot it's well worth the $3, and not that hard to do other than the float bowl screws.

[JOHNDOE83]

One jet size is meaningless and almost not even worth doing.

A 42 pilot will take care of your backfireing, you might "might" need as much as a 170 for your main jet.

If you put a 165 in and you still rev out fully I would just leave the 165 if thats all you buy, if you buy jets to actually jet, I would buy them from 160-175 in incriments of 5, I doubt youll need any higher.

Start with 175 and try to rev out to max rpms while rideing, if it stutters and doesnt fully rev out in the top rpms, drop down to the next lowest jet size "170" till you can fully rev it out.

My guess would be 160-165 is the sweet spot but you have to try it first to be sure.

[erik420]

Thanks for the reply guys. I have been looking online on a bunch of forums and I am going to get a 42 pilot and mains from 160 to 175 all. Going to order them this week and start fat and work down. More input is always welcome.

Erik

[Drfat400ex]

Funny, I had a 158 before and myn was running rich as hell, looked like a friggin deisel when you started it cold for smoke, and fouled the plug at least twice a week, then I dropped one meaningless size and now the jetting is spot on. Just saying.

[Crosshairs]

I have pretty much the same setup...and EHS lid with a full FMF exhaust....
I'm running a 42 pilot and a 158 main and its spot on....

[erik420]

Thanks. I will also pick up a 158 just to be safe. Anyone else have input? If so let me know. Oh and happy easter everyone.

Erik

[erik420]

I just ordered a jet kit and new pilot jet from jetsrus.com. I will post my final jetting sometime in the next week or two.

Erik

[erik420]

I jetted it this morning. Ended up with a 42 pilot and a 160 main. Seems good but I will not know for sure until I go riding somewhere where I can open it up. I live on a dead end street and can hardly get going in 3rd without getting people mad. It starts WAY easier with the 42 pilot! It did not backfire or stall one when I was warming up. Hopefully I can go riding tomorrow because I got a bunch of traveling to do in the next few weeks for work. I will update when I go for a good ride.

Erik

[TheAwesomehonda]

Sounds good but remember it can run great and still be lean in the main jet which would cause over heating. Just check your spark plug after you ride.

[erik420]

Yea thats what I plan on doing. Its got a new plug in it. It does not pop on decel anymore and just seems ro run better. Going to buy another plug also as a spare incase I have to change the main again.

Erik

[Crosshairs]

Originally posted by TheAwesomehonda
Sounds good but remember it can run great and still be lean in the main jet which would cause over heating. Just check your spark plug after you ride.

Unless he does a plug chop, checking it after a ride will tell him exactly nothing about the main jet .