416 Jetting

[FBRacing76]

Ok guys I am wondering in the area of what my 400ex is gonna hafta be jetted. I dont no my elevation but I live in Eastern Ohio. My mods are JE 10.8:1 Comp Piston, White Bros. Slip-on, K&N Airfilter, Web Cams Camshaft not sure of that matters. Can you guys help me with my jetting an what its suppose to be. Thanks

[cals400ex]

we could always guess, but jetting is trial and error. with the airbox lid on and in the colder months, i would try a 158 keihin mainjet. you will probally want to move your needle clip to the 4th position. also, a 42 pilot should work just fine. start with your fuel skrew about 2 turns out. these are just guidelines and some tweeking may need to be done.

[Quadfather]

I live in norther OH, have a JE 10.8-1 (416 kit), K&N, Yoshi slip on, and I am running a 165 main, and stock pilot jet.

[JP400ex]

I have a 416 that the heads been ported on it and has a web cam. The guy i got it from had the stock pilot #38 in it and like a #204 Main Jet. I also have a FMF Titanium pipe and silencer on it. You have to run it with the airbox cover off or it runs rich.

Heres my question, and i know already that the fmf pipe is a great mod, but im considering putting a stock exhaust back on because i live in the city and like to take it for the occasional ride down the street. With my head being ported im probably not going to want to go back down to the stock main jet. But if i stuck the stock exhaust back on what size would you guys try first???

[cals400ex]

Originally posted by JP400ex
I have a 416 that the heads been ported on it and has a web cam. The guy i got it from had the stock pilot #38 in it and like a #204 Main Jet. I also have a FMF Titanium pipe and silencer on it. You have to run it with the airbox cover off or it runs rich.

Heres my question, and i know already that the fmf pipe is a great mod, but im considering putting a stock exhaust back on because i live in the city and like to take it for the occasional ride down the street. With my head being ported im probably not going to want to go back down to the stock main jet. But if i stuck the stock exhaust back on what size would you guys try first???


first off i didn't even know they made a 204 mainjet. :huh
what brand jets you running?? if you do have a 2?? mainjet in, your too big. there is no reason you should be larger than a 170 at the biggest and i wouldn't ever go that high with a mildly built motor. i would run around a 162 with the airbox lid off with the fmf pipe and maybe a 160 with the stock pipe. these are just guidelines though. you are killing your power using that large of a jet unless you have many many more mods than you listed. good luck

[kargaaro]

158 main
45 pilot
Needle - stock setting

[skemp]

Originally posted by JP400ex
I have a 416 that the heads been ported on it and has a web cam. The guy i got it from had the stock pilot #38 in it and like a #204 Main Jet.

Yikes. You have no idea how much that is killing the power.

[BIGRED400]

I have a JE 11:1, HotCams Stage 2 , White-Bro's w/18 disc, I have a K&N 170 main.(reccomended)..I live in Fla..altitude is everything w/Jetting ......my problem is running straight 100 octane ,it's hard getting a good plug reading....I think I am gonna start 1/2 93 and 1/2 100 mix soon ....I think it'll help out on plug readings....100 burns real clean ....What do you think?????

[JP400ex]

ok.... well, i guess i need to pull the main jet out and verify. He told me it was a 204 but i haven't actually seen it for myself. Im guessing that he was wrong because the bike doesn't run bad at all. It did a little bit when i had the airbox cover on but now that its off it screams. I will post tonight after i check.

[speedy400]

mods on sig, its jetted for winter..-
Dynojet 175 main
dynojet needle 3rd position
screw 3 1/2 turns out
45 pilot
I believe its just about perfect, my elevation is about 200 feet
-darren

[JP400ex]

Well, I did some playing with the jetting and with the fmf pipe on it i dropped down to a 190 from the 200 and then down to a 185. When i put the 175 in it it ran really lean. as soon as i would hit the gas and let off it would pop like crazy, even with the airbox cover on. Im not real sure why i need such a big jet in there when you guys are all saying 170 max.

[cals400ex]

try putting in a 42 pilot first. with a modded bike, i imagine you need to have your clip on your needle in the 4th position. i assume your using keihin jets and not dynojets. i still say your main is too big.

I'd say going up 1 size on the main would do it. That's all I did.:)

Installing a 42 pilot is a good idea too, even if you keep the choke in ..:cool:


I run a 155 dynojet right now with all my motor mods.