Jetting for dummies!

[MAaudioX10]

Well, just picked up an 02' 400EX . When I bought it it had a K7N filter, CDI, and FMF Quiet core muffler (which was hollowed out).

So, I just bought an HMF slip on for it and now it seems to be running lean, which makes sense because I would think that HMF flows better.

I live in Iowa and my elevation is 3000 ft. With the old setup, it had a 170 dynojet and it ripped pretty good. I increased to a 175 keihn. Seems to have gotten better but, I have an annoying off throttle bog.

What do I need to do to cure that?

[nosliw]

move jet needle clip down a few notches to richen up the 1/4-3/4 throttle range, and maybe go with a 42 pilot jet while your at it.

[2001400exrider]

i got that same bog off the start and will be upping my pilot to a 42, should fix it....

[MadMax27]

Ive got a HMF full, 180 main, needle clip on 2nd to richest. 42 pilot. If I take the air box lid off, she runs like a raped ape, But pretty lean. With the lid on, shes plenty rich. I took the snorkel off, which I didnt want to do, and nows its closer, I think Im gonna drop to a 175 main and see how that helps. I also should set my air screw more accurately, instead of "3 turns out" I should set it for highest smooth idle, then change the idle screw to where I want it. Then see how it is before I drop my main....I just cofused myself..:p

[2004exrider]

droppin the needle down three clips sounds pretty common for the 400. when i did the mods to mine i only changed the main jet and put in a #42, never dropped the needle or adjusted the idle im startin to think i should. it runs good already but i guess i should?

[250rAL]

Originally posted by MAaudioX10


I live in Iowa and my elevation is 3000 ft.

The highest point in Iowa is 1670'. What are you smokin'?:D

[meanyellow03ex]

I've got the mods in sig and use a 170 keihin, stock needle position and 3 turns out on the screw. Was dyno tuned and air fuel ratio was between 12 and 14:1 across the board. Oh and stock pilot also.

[MadMax27]

What Ratio should you be lookin for idealy? I can prolly get my hands on an air/fuel gauge....

[meanyellow03ex]

Ideally 13:1 is good. Perfect is 14.7 : 1 but you'd rather be a hair rich than lean. The ratio changes depending on various conditions so you want to error on the safe side. With a 155 jet my machine was running 16:1 at 6000 + rpms. It ran good, but may end up with engine damage over an extended period of time.

[MAaudioX10]

Originally posted by 2004exrider
droppin the needle down three clips sounds pretty common for the 400. when i did the mods to mine i only changed the main jet and put in a #42, never dropped the needle or adjusted the idle im startin to think i should. it runs good already but i guess i should?

I guess some pretty good chit! LOL...well that is news to me! Everyone I ask around here says 3,000.

Where would I go to find out for sure what my elevation is?

By the way, I think I got her figured out. Went back to a 170 dynojet, moved needle down a notch, richened, and upped the PJ to a 40. I also forgot to mention it has a modified airbox lid. Essentially, it is an open airbox.

I no longer have the bog in the low end and it has excellent mid range throttle response. Won't be til this weekend before I try it out.