I was just wondering what the power differences are between jetting the carburater (is that spelled right?) and installing a 331 big bore kit? And question 2 is..if you install a big bore kit, it is also recommended to jet the stock carb? or not?..or for that matter..should one also make changes to the air and exhaust after installing a big bore kit?


Basically, if i install a big bore kit, do i need to touch anything else? or will I achieve comparable power gains just from the big bore kit as jetting, new exhaust, increasing air intake, etc

 

Changing any one of those things, will require changing the others as well. Meaning that to do the
big bore, you will need to jet the carb, it is even recommended by most that have done so, that
you swith to a different carb alltogeather, as the one that is on currently is very small. Also being a vent
slide instead of a direct pull slide or pumper greatly hinder performance as well. Anyway, just bolting
on a big bore to a stock bike will not run properly, certainly not up to its full potential. But if you do
stick with the stock bore, you can gain a fair amount of power from a dynojet kit for a klx300
(others will work fine, I have just always liked dynojet kits) Your results will be best if you open
up the airbox (remove snorkel, drill holes, or just remove lid alltogeather) and replace the exhaust
with one of the many slip ons available, or a full system. Any time you increase the amount of fuel
the engine intakes (ie, carb kit) you also have to increase the amount of air that can get in, and the
ability of the exhaust to get out.

 

I agree with maniac, if you change one part of the equation, you'll most likely need to change another part. If you are contemplating a big bore, then doing all four mods (intake, carb, big bore, exhaust)together will give the most gains and will cost around $1500.

The basic path that I took was:

drilled exhaust -- airbox mods: filter, kdx snorkle, desmog, external crankcase breather -- drill/rejet stock carb

Muzzy full exhaust -- rejet stock carb

Mikuni TM34 pumper carb -- jet for setup

331 big bore - rejet for setup


Mixed in there was an assorted of trials associated with the airbox lid/snorkle configurations. Currently I'm at airbox lid on and snorkle removed.

 

Thanks guys...kinda dumb question, now that I think about it...just trying to plan a winter project, but would like to have all my ducks in a row, and parts ordered long before I see snow. I think for cost reasons, I'll do the carb jetting, exhaust, air box and maybe a couple other little changes and see how I like it.

If I install a jet kit, aftermarket exhaust, KDX air snorkel...I know the response of the bike will be better, but does it affect the top end at all?...will it be a little faster? just curious about that part of it as well.

 

It actually will increase the top end a little, because in stock trim, the engine does
not have enough power to carry 6th gear up very high. You will notice now that
you have a very hard time maintaining 7,000-9,500 rpm in 6th, after doing what
you plan to do, it will rev out 6th much easier. (just my 2 cents, but dont bother
with the kdx snorkle, it works fine, but save your money and just rip out the
stock one and hog out the hole)