What main jet to use with a K&N filter?

[BeatYourTruck]

I want to toss the stock air filter setup for a K&N setup like this:

http://www.cartpartsplus.com/universal-k-n-filter.html



I was wondering if anyone has some experience with what main jet is best matched to it? Stock exhaust and 20" tires. Yamaha G14.

Thanks for any input! Side note: I emailed Carts Parts Plus and they replied with info on the jet size when used with an aftermarket exhaust but did not reply when I asked about this filter with the stock exhaust.

[bansheemxer]

You could most likely use a #125 up to a #135. I am running a #135 with a custom exhaust so I would think to try a #125 or something close. Put a new spark plug in and run the engine till it's warmed up and check to see the color of the spark plug. It should look light tan in color. If it's black then I would put the next size smaller jet in. If it's white, go bigger on the jet. The jets should be about $3 at your local ATV/motorcycle dealer parts counter. Just be sure to take your stock jet in there and then ask for the above sizes.

[BeatYourTruck]

Thanks very much for the starting point!

Any pics of your custom exhaust? I have access to the materials and some guys who can help me with one....just looking for what others have done and any input/comments they have on their system.

[bansheemxer]

http://www.buggiesgonewild.com/gas-y...ted-89-g2.html

these are old pics but it gets the point across. I just bought a muffler from a kfx450 to replace the xr250 muffler. I guess I will see how it works out.

I would for sure recommend getting the k&n precharger if you plan on running arould any dusty trails or even gravel roads. Or plan on cleaning your filter after every ride.

[BeatYourTruck]

oh yeah....prefilter for sure. I also thought about modifying the stock, under the seat, air intake to supply it with cooler (and slightly cleaner) air, building a little air box of sorts for it , etc.

Very nice cart!

My buddy builds custom race 4 wheelers and has already offered to make me some arms etc to do something similar to what you have done. But for now, I am sticking with the cheap lift! LOL Thanks again for the pics and for affirming what I had in mind is possible I appreciate your time.

[sho305]

When I modded my stock filter box I had to hog out the main until it ran right, I used a torch tip cleaner to file the jet out.

When I put a clone engine in a G9 I picked up a car airbox at a boneyard and used that. I put 2" pvc under the frame to a muffler clamp welded on near the gas pedal, then a 45 up to under the cubby area behind the front emblem. So it gets clean air from there to the airbox mounted near where the stock one was. Filters are $7. I was tired of plugged filters.

[BeatYourTruck]

Luckily, my 4-wheeler buddy has a massive collection of Mikuni jets....like about 500 different sizes LOL I am going to grab a handful of jets from him to do my tuning.

I like the snorkel idea!

[BeatYourTruck]

Just as an update in case someone is looking to do the same thing one day, I picked up 124 through 134 main jets to try with the K&N and stock exhaust. 124 is too rich. Plug is black and has major hesitation bog on take off. Once it gets going, it is OK but you can tell it is running way rich.

I will go back and grab some smaller jets (110 through 122) and post up what worked out. Stock main jet is 102.5 for reference.

[bansheemxer]

That's crazy how much bigger you can go on the main jet when a free-er flowing exhaust is used. I have been playing it safe by running the 135 jet since it has been so hot here in Oklahoma. It is starting to cool off outside now so I will probably lean mine out to a 130 jet pretty soon. Let us know how it turns out!

[sho305]

You should see the jet in the 16hp clone I did with a car muffler and car airbox with 2" pvc tubing. It is WAY larger than stock. It was so large it started to miss at low speeds and I had to make another a little smaller. I think it needs the air jets changed in the carb but not sure what to do with it, hard to find info. Rather put a slide carb on that is much more adjustable....after I find time to figure out how to make a new manifold that turns the carb the other way lol.