not revving up

[fastboarder]

400ex 426 big bore
stage 2 hotcam
uni filter
amr coil
it goes but it starts backfiring like a fourth on the throttle dont know if its jetting
its at 148 main 38 pilot it idles fine what should i do go up a couple sizes on the main or what any help please

I had the same problem in the summer. But back then i only had an exhaust. What i did was change everthig back to stock and then saw if i still ahd the problem. I then noticed my idle screw was gone. So Makesure you double check everything espically your carb, and deffiently change the jetting.

[rcatvrider]

It's been a while since I dealt with carbs but both of those numbers seem awfully small for a bored motor.If I remember correctly, most run higher than that with simple mods like an exhaust and filter.

[siggy konowaluk]

yeah try chaning the jetting that might help you out.

[rcatvrider]

As in richening it with larger(higher number) jets in case you didn't know. Not being a jerk, just trying to help. Maybe someone more knowledgeable with built up motors can chime in.

[fastboarder]

yea im about to put a bigger jet in it. dont know what size yet it also has a full exhaust system

[guenther]

Give 155 main and 42 pilot a shot. It should be pretty close.

[-TheDude-]

poss fouled spark plug

[honda400ex2003]

whats your elavation and such too, also are you running a dyno jet set or a keihin set of jets? I run a keihin 170 in my 416 at about 1500 ft. i would say you need about a 175 at least. i missed your mods though, i would start with a 180 main, 38 pilot or a 42 pilot would be fine, the needle on the 3rd clip position from the top( this should be stock position) and about 3 turns out on the f/a screw with a 38 or about 2 with a 42 to get you started in the right direction i guess. Do some searching and see what guys with 426s are running for jets. some of them get pretty big. steve

[honda400ex2003]

i didnt see an exhaust or anything listed so i would say go with about a 170 to start and see how it goes. Check the plug and go from there though first. steve

[atv fan 28]

148 sounds WAYYYYY Lean!!!

[fastboarder]

yea i just put in a 160 and ill see how it goes tommorow might get a plug to so ill see what happens then.

[jasonwayne222]

i went for a ride on sunday and all of a sudden it started doing the same thing, i knew it was something clogged in the carb, so i made it back to the truck and went through the carb, which only took a few minutes since ive done it so much, and everything looked good, well finally after a few minutes i noticed that the plunger "part that the needle rides in" wasnt pullin up when i gave it throttle, well the screws inside had backed out, so i through some locktite on them put it back together and was good,

so the easiest thing to do to check your carb is make sure the plunger goes up and down and that your accelerator pump is spraying all at the same time when u give it throttle, two things right off the back that u dont have to take the carb apart to see.

I have a rubicon and the needle and plunger are vacuum operated but the 400exs are a mechanical linkage.

[fastboarder]

put a new plug in and the 160 still hasnt changed so idk maybe the needle isnt going up or something ill have to check that

[bigbad400]

yeah make sure things are working right but i think you may need to move your needle so it sits one notch higher, sounds like it to me.

[fastboarder]

got it to work today had to adjust the thing the jet sits in lower it wasnt getting any gas then put a 170 in it might drop it down a little bit tho seems like to much now.