Help! 400ex problem

[unitednations]

I juts got my ex put back together and when im driving it at a constant speed, it spits and sputters alittle. Its not really bad but its noticeable. Losses alot of power with midrange

I put a 11:1 piston in it
Stage two hotcam
and its piped with a HMF

jetted 42 main
1 clip richer (not sure if that was up or down)
and 162 main

Runs 93 pump gas

Any Ideas what would cause the sputtering, It only has like 1 hour on the rebuilt motor

[hornetgod13]

Air box lid on or off? You said at a constant throttle setting but is it mid range or wide open? Which direction did you put the clip on the needle? You might have went the wrong way. The clip should be on the 4th slot down. There is no such thing as a 163 sized jet. They run 148, 152, 155, 158, 160, 162, 165 and so. If your lid is on it might be rich on the top end (main jet)

[vAnS_77]

Sounds like its running abit rich. Either that or your connection to your exhaust to engine or header to siln. is gapped.

[unitednations]

oops its a 162, sorry I must of wrote that fast. Its midrange where it sputters. I haven't went pass half throttle yet. I moved the clip one down from stock. My lid is on, but i put in a K and N air filter and it might of made it alittle worse.
Also it loses alot of power in the midrange. it feels like its hard to go.

[rideracelivemx7]

take the lid off for one. for a jet that size. mehh its boarder line on if it should be on or not. to be honest thats exactly how my bike was when i first got it running. it wore in that much more the next day and it was fine. what are you running on the air screw? that might be it. im 2.5 out.

[hornetgod13]

Take the lid off and see how it runs. If it improves either leave the lid off or lean out the jetting.

[UNBROKEN]

i agree it sounds rich but still even with the lid off a 162 seems pretty big ure elevation shouldnt be much from mine and i have a 42 pilot and 155 main with my LID off and my runs perfect no bog

[unitednations]

I took the lid off and took her out, and it might of helped alittle but not very noticable. Its not really bogging its more just an uneven exhaust flow it sounds like crackling and spitting/sputtering. sometimes it does slow the Bike down alittle. When i let off the throttle than hit it agian it sputters quickly before it takes off, Still it doesnt slow down the bike.

Would it be my main jet, if it does it on 1/4-1/2 throttle, I havent opened it up yet ?

and elevation is around 900 feet

[hornetgod13]

Idle - 1/4 throttle: Pilot Jet & Fuel Screw
1/4 - 3/4 throttle: Needle
3/4 - Wide Open throttle: Main Jet

[unitednations]

alright i think im figuring it out. It cuts out on idle to 1/4 throttle , should i go ahead and get a smaller slow jet, or change the air/fuel screw. Its got a 42 in it now

[rideracelivemx7]

I wouldn't jump the gun on the pilot jet quit yet. I would mess with your fuel screw first. that makes a huge difference. I ran that same set up for jetting just with a 170 main and with out the exhuast then. and it was on the stock motor. but I had to really mess with the jets. so I don't think it would be your pilot jet. try that and see what it does. you running stock bore? if the fuel screw doesn't work try the next size down and next size up. interchange them. also put the clip back in the stock spot.

[unitednations]

i turned the fuel screw in a half a turn, it made no difference.


I have a 162 main
1 clip down from stock on needle
42 pilot
fuel/air screw 2 turns out
KN air filter with lid removed

Bogs( more of a jerk feeling from wheeler) on low end and mid range with spitting a sputtering randomly
really black stuff in exhaust


what changes should i make?