Jetting/air box mod question

[Phil McCrackin]

Have an '02 KDX220 with FMF Gnarley woods pipe and Powercore II silencer. Ran fantastic with stock jetting. Did the airbox mod today by cutting the snorkel tube that extends into the box and subsequently drilling 7 1/2 inch holes into the lid. Idles fine and has good power to a bit less than mid throttle, but above 1/2 to wide open, it's just flat!! It's loudly drawing air, but the acceleration is non exsistent. Is this just a main jet and possibly needle clip position issue or should the pilot jet also be considered?? Any help is greatly appreciated.

 

[r6demon]

from my tiny understanding of jetting it sounds like your main is to small. The pilot jet is only really used to idle the bike. search the forum for carb advice to see what main you should use

 

[matt-itude]

too small of main should rev quick then go flat (im thinking too lean also) it sounds fairly lean so im thinking if it was me not only a larger main but i would fatten my needle one to be safe. you can always lean it back out (I mean the needle not the main) if you like it better.

 

[Phil McCrackin]

Matt,

I agree with going up on the main, so I will go from the 145 to a 148. I will also check the needle clip position. Wouldn't going to a larger (fatter) needle lean my condition or am I not understanding something here?? Or when you say "fatter" do you mean "richer" and go a size smaller??

 

[dsndblm]

Yes a larger diameter needle will lean the mixture. I think matt-itude meant to fatten or richen the mixture by using a smaller diameter needle. Smaller needle allows more fuel to be fed through the main to the engine. Lowering the needle clip will raise the needle out of the main jet richening the mixture. There is much more going on than that unless you are at WOT. Did you read the jetting and needle sections on Daves tech tips. If not take a few and read the tips. It is worth the time!

 

[matt-itude]

yes I did mean mixture not actual needle size and untill your out of adjustment (as far as # of positions on the needle) or looking to really fine tune you can probably get it there with the stock needle by just moving the clip. typically when you go a jet size or two you need to move the needle one clip position richer or leaner coresponding to your jet size (if your main needed to be richer your needle probably will need to be richer also).

 

[Phil McCrackin]

I figured I'd mess around with it today. What a time consuming pain in the ass!! Went from the stock 145 main to a 148 and left the clip position in the stock location, which was in the middle. Seemed to run OK and didn't flatten out at WOT. Next, I removed the 148 and tossed in a 150, leaving the clip in the center location. Ran well there also, but smoked like a bug fogger!! So, I moved the clip to the 2nd from top positon to drop it down. Still ran decent but smoked rediculously. Sooooo, back to the 148 with the clip in the center postion. No smoke, but that worried me, so the final setup is the 148 main with the clip in the 2nd from the bottom position. Seems OK, but man, it's hard to tell if it could be better. I'd rather be a little rich than too lean and unfortunately, I can't do a throttle chop where I live. It's bad enough that I'm tearing through my neighborhood trying to get this thing dialed in!! Any tips or should I leave it alone? I ordered 2 larger pilot jets. Should I dive into those as well??

 

[matt-itude]

I would do some reading as previosly mentioned to refamiliarize yourself with the procedure and ad just your air screw and see were it ends up to determine if you need to change your pilot jet.

 

[john_bilbrey]

I've got the same setup as you on my '03. I don't remember where I ended up with final jets though...I'm pretty sure if you search under my name you'll come up with the final jettings. The only difference is that I tossed the entire airbox lid. Also, remember that all bikes (even the same make) are different. I was not as rich from the factory as the majority of the folks here, ended up with a "lean bog" and almost cooked the old girl. Luckily a plug chop told me (along with the help of the nice folks here after describing my symptoms) I was way lean...

 

[Phil McCrackin]

Guys, thanks for all your tips. I finally got it hammered out. Went with a 148 main, 42 pilot, clip in 2nd from top and A/S at 1.5 out. Still fiddling with A/S, but transition is nice between circuits. Funny how the clip position made such a significant change. Had it in the middle initially and it bopped-bopped at 1/4 to 1/2 with poor transition (rich). Moved to 2nd from top and it was really amazing how it smoothed out. Thanks again.

 

[canyncarvr]

Take a look at CDave's site for more information of jetting the 220 to different levels of often done modification.

His site is linked in the 'Every kdx rider should read...' thread at the top of this forum.

Note the 220 is flat on top in most any form....and the -35 pipe doesn't do anything to make that better. The small PWK has a lot to do with it. You would notice a considerably improved upper power band with an RB-Designs massaged carb.

Not much you can easily do with the port timing on the 220.