I just recently got back into the sport atv world and picked up a 05 KFX 400. I put on a Moose racing by BUB slip-on exhaust and a rev box. I was wondering if anyone has done these mods and what jetting you used? Is there a jet kit out on the market for dialing this in? Any info would be great.

Thanks

 

I'd go with either a 150 or a 155 main jet. Thats what I ran in my old KFX when i had a Muzzy slip on seemed to work really well. Now I've got a '06 DVX w/ LRD Pro-4 exhaust and they say to run a 175 main jet so that's whats in that bike. Most jet kits are just a great big waste of money unless you are really diving into motor work I'd just go to the dealer and buy a few Main jets and play around with it might cost $10 hope this helped!

 

That's what I was thinking of doing. I heard to run a 160 with a slip on. Think I'll go and pik up a few jets and try that. Do you have any ide on what the stock size jet is? With the rev box I did notice if I "blip" the throttle it will hesitate for a second then rev. I'll pick some up tomorrow and try it out.

thanks!!

 

I want to say the stock jet is a 136 but I'm not for sure. Sometimes the screws in the bottom of the carb (float bowl cover) are hard to remove besure to go to Lowes are Home Depot and pick up some M4 socket head screws much easier to deal with then those cheap *** philips heads they come with.

 

i saw a couple of dynojet jet kits on e-bay. somebody in my town has one cheaper than new. jetting is everything. i have always tryed to stay on the rich side . seen pictures of what a lean motor lookes like.

 

With my HMF their recommendation is a 170. recommendations are only starting points, so you really got to dial it in yourself. Elevation is a huge factor. I also think they assume you'll be running no lid, so it may be a little rich. I left the lid on, but removed the snorkel. The 170 jet is a little rich for me, but it's such a pain in the **** that I just left it because it's real close. I could probably use a 160. there was no need to go up on the pilot. I just drilled the plug and adjusted it.

I just bought individual jets, much cheaper. The only benefit with the dyna-jets I see is, I believe they also come with an adjustable needle (which only works with their jets).

 

are you going to keep it more of a trail bike/playbike?? if you are wanting to up grade, the yfz 39mm carb really wakes up a 400!!!! you can also find them on ebay, i got mine for $150.

 

Thanks for all the info guys!! I installed a 160 with the air box removed and WOW what a differance. I may be slightly on the rich side but ok with that. My bottom to mid is killer and a little flat on top. Does that mean too rich or lean? Also the bike is more a fast trail play bike. When you adjust the air screw what did you go with? I read where you need to remove the plug and adjust it to 3.5 turns out with the dyno-jet kit. Would it be around the same setting? I'm use to the old school 2 stoke carbs where you went 1.5 out and went from there. Once again thanks!!

 

If it's good on the bottom, you may not need to adjust the fuel screw.

0-1/4 throttle is dependent on position of fuel screw
1/4-1/2 throttle is dependent on pilot jet size

1/2-3/4 throttle is dependent on either needle taper, or clip position
3/4-full is dependent on main jet size


If it pops after go wide open, then let the throttle off than it's definetely to lean on the fuel screw. It's not the only indicator that it's lean, but it's a pretty positive one.

 

Hey

I just got done putting on the new K&N airbox top and filter...I jetted my bike out with a 160 and so forth and it seems to be running real smooth. What an amazing difference from such a little change..So I am taking it out this weekend and I was told to look for any problems after its been heated up....Should i wait to hit the trails deep and hard tell after she has warmed up or am i cool just taking off?

Kat