[carb mod] - ATV Riders Forums - Honda, Yamaha, Suzuki, Kawasaki, Polaris, CanAm, Arctic Cat, Kymco ATVs

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carb mod
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Posted by: jeff32073

I am new to the 300ex. I just bough one with a super trap exhause, k&n air filter, and the air box lid off. My question is for the carb should i buy a dyno jet kit or a 400ex carb. I dont have any engine work done nor do I want to do any to it. Also is their a advantage between just buying a bigger jet or do I need this dyno jet kit?

Posted by: SET THE STAGE

if you don't mind taking the time to try to tune it in, get a 400ex carb. i have one and love it.

Posted by: jeff32073

Thanks. Would that be a much larger difference over just doing a dyno jet? What size jet would I want for the 400 carb. Again my onlymods would be no air box lid and supertrap exhauset,k&n filter

Posted by: SET THE STAGE

you'll see a much bigger difference from a 400ex carb rather than a dynojet because dynojet isn't really supposed to be an improvement. at least, in my eyes, it isn't. it's just an "easier" way of jetting your carburetor. i think it's more complicated because it uses completely different numbers and everything. only improvement you'll actually see with dynojet is the same improvement you'd get from just jetting your carb with the ones that are actually made for your carburetor.

with the 400 i'd start with the stock 155 that it comes with and go from there. i'm running a 175 (i think? maybe one up or below) but i have more stuff done. just start with the 155, start it up and ride it if possible. be soft, though. check your plug and go from there. do you know how to read plugs for jetting?

Posted by: 2muchquad

the 400ex carb will make a nice improvement even for your relatively stock motor.Its a worth while mod.Its been a popular mod so you'll be able to gets lots of help here with jetting etc

Posted by: JohnT_98300EX

I like my mods to be cheap and simple. All the jetting that was needed for my ride was an increase in main jet.
And because I ride a lot and in the real world (lots of dust and dirt) I went with Uni filter vents for the air box. I can't see dragging sand through my engine. You can add as many of the 1 inch vents as you need.

Posted by: jeff32073

thanks for all the help on this. Is there a certain year 400ex carb Iwould want? I saw one sold on ebay cheap that was off a 2000 and i lookin up specs which said 35.5 and a 2004 went for almost double and it said they were 38. Is this correct info or just buy whats the better deal?

Posted by: SET THE STAGE

the earlier the year, the better. look for one off of a 2004 or earlier. the 2005 and up years don't have an adjustable needle.