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My bike is a 98 kdx220r with fmf pipe and silencer, boyesen power reed, and modified airbox lid. I just got my carb back from Fredette (was ported from 33-36mm). I asked them if they could jet it for my setup, and they said they could get it spot-on. I had a 145 main jet and 42 pilot jet in before, and they put a 160 main jet and 45 pilot jet in.... now the bike does not accelerate if you give it gas... it just bogs, not like the bog you get with a dirty carb, but more like detonation or something. What should I do?

160 seems rich for the main jet on this? but Fredette is the expert on these bikes!

Should i put my 145 main jet back in and see if it runs better?

I don't know if the main jet is the issue though because this is happening after about 1/4 throttle which is where the needle controls things right?

Rejet it. I'm not really understanding the reference to detonation, but you could revert back to your old jets just to see if it's better, just don't ride it like that for long, it may be too lean for the new setup.

Well after 1/4 throttle it doesn't accelerate, just makes a stuttering noise

I've had that problem. It was when my bike was cold and had stock jetting. You need to re-jet, period.

So Fredette didn't get close to being right on the jetting?

Anyway I have different problems. I went to put a different main jet in, and the little pin that holds the carb float in fell out onto the ground. I slid it back in, but apparently it doesn't want to stay in because i put the carb back in the bike and gas poured out of all the tubes. I opened the carb back up and that pin was out again.... what holds it in?

In a recent thread by wudscrasher re: mileage, two members with bored- out carbs gave their mainjet sizes respectively at 150 and 158, so your carb is not that far off. Don't put your old jets back in, you might seize up your engine.

Sounds to me like you might have a machining chip or other particle blocking fuel, or more likely something is mis-installed like the needle position. Quarter throttle on up is normally a needle issue, you might just want to raise it a notch and see what happens and go from there.

Do some research here for like-altitude jetting in the RB mods forum...I bet you can get it fixed easily.

Well now gas is pouring out of the carb.... Out of all of the tubes... i figured out that the pin for the float is held in by the carb housing itself... so that isn't the problem... I wish I knew more about this stuff because I'm lost?

Your float valve isn't seating. Assuming you didn't bend anything, it is either cocked, binding, or has a foreign object lodged in the seat so it won't seal.

Never mind, I found out the acutal thing that seats in and blocks gas off fell out!

But I still need to figure out why its running so bad...

How do I adjust the needle?

Maybe it isn't a jetting problem... I don't see how Fredette could be off by that much and from what I have read it seems to be pretty close, close enough that it shouldn't run this bad

What a shame that Fredette jetted a 220 carb for a 200 bike. He jetted your carb for a 200cc motor and not the 220. Your port timing is much different than a 200 and needs leaner jetting. Your bike can't be jetted that rich. I would call him up, explain everything to him as you did to us and see what he says. He should be happy to get this straightened out for you.

BTW, just curious, but why did you go with Fredette for carb work instead of Ron Black?

Because I am a cheapskate :)

So with my 220 and the mods I have, what jetting do you think I should run for main and pilot?

skipro3 wrote:What a shame that Fredette jetted a 220 carb for a 200 bike. He jetted your carb for a 200cc motor and not the 220.

I don't know if that is true....as I noted earlier, at least two 220 owners here with bored out carbs are running similar jetting, one with a 158 main and a 45 pilot (krazyinski) I would certainly give Fredette the benefit of the doubt at least until you fiddle with the needle setting.

To do that, you simply unscrew the carb top cap, compress the return spring, unscrew the needle retainer in the bottom of the cap, pull out the needle and move the circlip that positions the needle down one notch, thusly raising the needle relative to the throttle body (which will richen the mixture), and replace. Kind of self-explanatory once you get in there.

Quoting Krazyinski; " thats on a 00 220 with ported cylinder, milled head, carb bored from 33mm to 36mm FMF desert pipe. 158 main, dem needle-2, 45 pilot. any smaller main and it falls off or flattens out on the top. "

Sounds like it has much in common with your bike - except mebbe the porting?

That was my point Gumby; porting (stock anyways) is mucho different between a 220 and a 200.

I say give Jeff a call and see what he has to say about it all.

Naahhhh,
raise the dang needle and see what happens. Remember the poster's comment about detonation sounds? Lean can very much do that... braaaaap, braaaap..... squeak!!!. At least he'll then have a clue as to what is going on, no?

So you think I need to riched the needle jet?

Well I talked with Jeff, he was surprised because thats the jetting he always uses and he said its usually close. He said to put the 145 main in and see if that is a step in the right direction. I did that and it runs a lot better. I will try
a 152 probably and see how that works

Well....I'll be darned. Looks like you're going to learn how to jet!

For jetting performance effects based in rough throttle opening terms, heres what you can go by most of time;
main jet : half throttle on up, less effect at half, most at full
jet needle: one quarter to three-quarter most effect at half
needle jet: one quarter to full, most effect at three quarter
slide cutaway: 1/8 to 1/2 most effect at quarter throttle - hmmmm
pilot screw and jet: closed to quarter throttle, most effect at closed.

Your original description talked about a quarter-throttle bog, if your statement was correct, reducing the mainjet to improve things makes me think something significant is still related to the needle or slide - I assume they put the right slide in? As you might notice by the approximations above, there is a LOT of overlap between carb elements in jetting... but the mainjet should not have an impact at quarter throttle...
Anyway... have fun...you'll jet like a pro in no time.

Jeff said the needle should be fine right where it is, in the middle position. With the smaller main jet the bike ran well, so I don't know if the needle is the problem. I'm going to play with the jetting a little more tomorrow

Do a search on this forum and you will find some pretty specific instructions on how to properly jet a 2-stroke bike. If you have questions, it's best to just ask away. If you have trouble finding the threads about jetting proceedures, ask about that as well. Good luck and let us know how it works out for you.

Here is the jetting procedure

http://kdxrider.net/forums/viewtopic.php?t=1156