Bigger Main Jet?

[rooster300ex]

How come the dynojet jet kit only comes with a 128 as its biggiest jet. i've seen some 300''s on here have a way bigger main jet then i have and have less mods then i do. i bet i need a bigger main jet to make mine run right. u can see my mods down below. do ya'll think i need a bigger main then a 128.

[skyhighatv]

does it run good now? what probs are u having? backfire,sputtering or bogging out?
let us know more.

[jak1389]

your sea level is wat determines what jetting you run with your mods. adjust your fuel screw to fine tune your jetting.

[rooster300ex]

well it cuts out at lil over 1/4 throttle when holding a steady speed, and the throttle response isn't that great and say i was powersliding in 3rd it kinna bogs. it didn't use to when it was stock, and sometimes it will make that air spitting noise through the carb.

[bwamos]

Bog at 1/4-1/2 throttle is a lean needle. Move clip down 1 (needle up).

Air being pushed back through the carb? If so, you're timing is off and that will make jetting really really weird.. lol.

[rooster300ex]

can rejetting make your timing get messed up or what. i had the whole engine rebuilt it should be at the right timing.

[jak1389]

no it wont mess up the timing but it could mess up the throttle response.

[prepracing]

just an FYI - dynotjet # sizes are different than other jet # sizes, such as khein jet #'s. That always causes confusion on hear on all these jetting questions

[rooster300ex]

u mean the timing being off could make it lose throttle response.

[jak1389]

Originally posted by rooster300ex
u mean the timing being off could make it lose throttle response.


most deffiantly.

[Jason250ex]

how do you move the "needle clip" i have taken my carb (250ex) apart at least 10 times and have never found an adjustment for it

[rooster300ex]

well thats bull**** the guy that rebuilt it should take a look at it and make the timing right. could your jetting be so bad out of tune that it makes a puff noise through the carb. it happens when i tap the throttle, it puffs through the carb and dies.

[rooster300ex]

if its anything like the 300ex carb the needle is in the slide. in the bottom of the slide in the middle u should see a small e-clip when u remove the slide arm. thats the needle move it down to richin and up to lean.

[bwamos]

http://www.atvriders.com/articles/jetting.html

I'd still put money on the fact that when they put your engine back together they got the timing off by a tooth. It's really not hard to do. If they had the slack taken out of the tentioner side instead of the front side.. it will put it out of timing by approx. 2 teeth on a 300ex.

It's also a quick easy fix.

Have you had it up to full throttle under heavy load? If your timing is off by a couple teeth.. ot will feel like you have power potential.. but oddly feels like your trying to tow another atv behind you.

[rooster300ex]

what do u mean under heavy load?

[bwamos]

Shift into 4th or 5th gear early.. and give it full throttle.

[rooster300ex]

oh i see. well i moved the needle down 1 notch to richen turned the fuel screw out 3 turns and cleaned the carb real good. i let it idle for awhile and it didn't cut out when i blipped the throttle. well see what happens when i ride it and get it hot.

[rooster300ex]

i let it idle for awhile and let it get warm and it didn't cut out when i blipped the throttle twice at about half throttle. just gotta ride it nedt and check the plug.

[bwamos]

Cool.. must just be jetting then.