KDXRIDER.NET

Hello everyone,

I recently picked KDX 220 and I'm having a real issue trying remove a bad stumble/breakup at 1/4 throttle. The bike did this when it had the stock pipe and jetting as well.

So what happens is if I take off lets say in the neighborhood stop sign to stop sign driving normal It will pull very hard to 1/4 throttle its hard to keep the wheel down but then it stumbles and then recovers as you accelerate out of it. If I hold the throttle at 1/4 in any gear is will continue to do it until I either accelerate or let off the throttle. If I turn the airscrew in and hold it at 1/4 throttle I will get a real bad flat spot and gurgle in that area, if I turn it out it will improve to the point where I can take the airscrew out where it run the best but will kinda feel like a misfire or rubber band feel at 1/4 throttle, it will surge then stumble over and over but very slight. There is no inbetween and I really feel I still needs to be leaner as its the best with the airscrew removedt. The plugs are black and oily, but have started to brown up with the 40 pilot.

At first I thought it was my pilot jet so I dropped a from 42 to 40. This did help as I got the highest idle at 1.5 turns out but the problem was still there but better. I kept turning the air screw and finally took the dang thing out. The bike runs best with no air screw but the stumble / break up is still there but very very slight now.

Obviously I'm going to clean the carb again and check my idle air screw passages and make sure i don't have a partial clog before I drop to a 38 pilot. But should the bike be able to idle with no air screw in it?

Stock jetting is 145M 42P R1137 needle 2 position.

Mods I have dont to the bike and current setup.
2004 kdx220
Desert pipe, snorkel removed and 607 reeds.

My current jetting is 145M 40P needle in top position runs best with no airscrew, idle does not hang at all?

Any advice or guidance is appreciated

Thank you

Try putting your needle in position #1 and see if it gets better. Either that or change the needle out for one that's known to work well in KDX's.

Welcome to kdxrider.

Moved to the general Q&A section. The forum you posted in was a reference section. Thanks.

If it's at 1/4 it's not the pilot causing issues (assuming it is the correct pilot). At that point its the needle. From your description it sounds rich so you would need to go to a leaner needle (larger diameter). Since you have the needle on the top clip (#1 position) you likely need to go to the next leaner needle.

bufftester wrote:If it's at 1/4 it's not the pilot causing issues (assuming it is the correct pilot). At that point its the needle. From your description it sounds rich so you would need to go to a leaner needle (larger diameter). Since you have the needle on the top clip (#1 position) you likely need to go to the next leaner needle.

You're correct, going smaller on the pilot slightly helps but only to a point. I pulled the carb and its clean as can be and the float is set correctly. I did drop to a 38 pilot, needle clip in top slot. its very close but a touch to rich still at 1/4 and runs best with no air screw.

So right now I'm running the stock R1173L needle top position. Can someone point me to a needle guide or recommend a few different needles to try.

Thanks so much

Bob

JD Jetting Kit. Excellent jetting instructions too. If you are running an FMF Pipe, they come with a good set of Jetting recommendations, too.

Sent from my CPN-W09 using Tapatalk

I think I’m just going to park the bike till I get the RB carb mod done. I’m assuming this should take care of my problem, ufortuanlty he is not taking on new work right now so I here I wait.

I had a similar problem with my 220 that I thought was throttle position specific but it ended up being rpm specific. When riding (like you mentioned at about 1/4 throttle) it would accelerate good, then start to stumble, but if I rolled on the throttle it would come back on power.

On the left side of the cylinder is the kips slotted cover. On the bottom of that there is a hollow bolt that contains a spring and ball. I removed the spring and ball, put the bolt with 2 brass washers back in and it was night and day difference. The bike accelerated much cleaner with no ill effects. It's like my bike didn't like being right between kips open and kips closed. I'm sure there's more to it with mine that I should have looked into (sticky valve or an ignition problem when the timing changes for the Kips opening) but I just serviced everything and was tired of the problem. Removing the ball and spring was simple, quick, and fully took care of the stumble. I read that Jeff Fredette recommends leaving out the ball and spring otherwise I never would've even thought of trying it.

Be careful if you do it that you don't lose the ball. You can always put it right back in if it doesn't make a difference but I feel like you should try it since you're going to wait anyway for RB carb mods. Since the bolt is hollow I wouldn't crank down too hard on it when tightening.


Heres the test I did that finally got me to looking into that...put the bike in third or fourth gear at only like 10 mph and then hold the throttle at 1/4 to accelerate. If would start to take off ok but then reached mid rpm and stumbled. Another test was to accelerate through kips opening so I was up there in the rpms, let off the gas, and then held it at 1/4 throttle for a second or two. The second test had great throttle response at 1/4 and that's when I realized it wasn't the carb.

John_S wrote:I had a similar problem with my 220 that I thought was throttle position specific but it ended up being rpm specific. When riding (like you mentioned at about 1/4 throttle) it would accelerate good, then start to stumble, but if I rolled on the throttle it would come back on power.

On the left side of the cylinder is the kips slotted cover. On the bottom of that there is a hollow bolt that contains a spring and ball. I removed the spring and ball, put the bolt with 2 brass washers back in and it was night and day difference. The bike accelerated much cleaner with no ill effects. It's like my bike didn't like being right between kips open and kips closed. I'm sure there's more to it with mine that I should have looked into (sticky valve or an ignition problem when the timing changes for the Kips opening) but I just serviced everything and was tired of the problem. Removing the ball and spring was simple, quick, and fully took care of the stumble. I read that Jeff Fredette recommends leaving out the ball and spring otherwise I never would've even thought of trying it.

Be careful if you do it that you don't lose the ball. You can always put it right back in if it doesn't make a difference but I feel like you should try it since you're going to wait anyway for RB carb mods. Since the bolt is hollow I wouldn't crank down too hard on it when tightening.


Heres the test I did that finally got me to looking into that...put the bike in third or fourth gear at only like 10 mph and then hold the throttle at 1/4 to accelerate. If would start to take off ok but then reached mid rpm and stumbled. Another test was to accelerate through kips opening so I was up there in the rpms, let off the gas, and then held it at 1/4 throttle for a second or two. The second test had great throttle response at 1/4 and that's when I realized it wasn't the carb.

Been out of town the past 6 days. Ready to get back to work and sort this out.

So last time I was out riding I was questioning this as well. Was it RPM specific or Throttle specific?. It's definitely 1/4 throttle in any gear at steady speed But this is also at least by ear the same rpm as well, So I still don't know.

When I moved the clip to #1 it was a really big improvement but still not right.

If this was a KIPS issue wouldn't it be all the time and not improve with jetting changes?

I will try what you said about removing the ball and see if there is any improvement.

If moving the needle clip to #1 made a big difference then you need to drop the main jet one size or switch to a different needle that's known to work well in KDX's.

SS109 wrote:If moving the needle clip to #1 made a big difference then you need to drop the main jet one size or switch to a different needle that's known to work well in KDX's.

+1 as noted a couple times above.

IIWM I'd probably get an R1174 (stock for the 200) and give it a try. It's got the same taper with a larger diameter. It's a tad leaner so I'd try it at the 3rd or 4th clip and go from there while leaving everything else alone.

bufftester wrote:

SS109 wrote:If moving the needle clip to #1 made a big difference then you need to drop the main jet one size or switch to a different needle that's known to work well in KDX's.

+1 as noted a couple times above.

IIWM I'd probably get an R1174 (stock for the 200) and give it a try. It's got the same taper with a larger diameter. It's a tad leaner so I'd try it at the 3rd or 4th clip and go from there while leaving everything else alone.

Thanks for the info on the needle I was thinking the R1174 would be slightly leaner but wasn't sure.

I was out testing today with Needle clip #1 dropping the main jet size didn't improve anything and bike runs best with air screw removed. Doing some plug chops in the problem areas i'm way to lean! If I go richer the problem gets worse.

I'm actually starting to think it is a KIPS issue. I removed the spring and ball. I lost the bottom end hit I had before but the flat spot really improved. It's a very smooth delivery now but you can really feel when the KIPS kicks in now and its clearly a problem when it opens. it almost feels like it is fluttering. I was also able to install my air screw again at 1.5 turns.

I'm going to tear it down tomorrow and see what I find inside. Supposedly the bike was bought and parked since 04 and ridden only a handful of times. Sure looks like it as its showroom new without a scratch on it. Maybe it's sticking from sitting all them years? I don't know but from what I read I should replace the piston while i'm in there, It has 170 psi of compression that seems good to me but I'm a kdx newb.

Ill update if I find anything.

On a KDX220R, I would. (replace the piston with aftermarket)

i agree with the piston change especially since you said you're going to tear it down. The compression is good but if you haven't seen some of the pictures of a 220 piston blowing to pieces...look it up. It was enough to scare me into a new piston before I even started riding mine.

I used the Tusk brand top end gasket set which I think is a good buy and nice quality for $17 at Rocky Mountain. It even includes the brass washer and two orings for the pipe. There are two other orings you should replace while you're in there. One is for the Kips slotted cover and the other is referred to as "packing" on the Oem top end diagram. It's just a small oring that goes on the horizontal kips shaft that runs through the cylinder on the right side. Both should be in stock at Rocky Mountain.

A service manual, a torque wrench, and a Motion Pro torque wrench adapter ($12, it's for access to the cylinder bolts) are good to have if you don't already own them.

This thing is officially driving me nuts. I did not put a new piston in it yet but I did have a gasket kit. I tore down the top end everything looks pretty and new with very little carbon on the KIPS. The KIPS valve look ok to me.

I put the bike back together with stock jetting but the needle clip in the top spot where it runs best and did a plug cop in the 1/4 throttle area where is has the issue. I'm not sure what to make of it. One side of the plug looks ok but the other side of the plug does not. Any plug reading experts can chime in? I'm thinking maybe its the jet block gasket?

Here are the pics of the plug.




I definitely have something going on. If I run the fmf recommended jetting for my pipe (stock jets but needle in #3) if bogs and wont move.

Any ideas?

Thanks

Update:

So I changed the jet block gasket and re-gained control of the air screw and the funny spark plug ring I'm assuming was the jet block gasket bleeding into the parth throttle plug chop is gone. The part throttle surging/miss is gone and all around much better.

I still have to run the stock needle (R1173L) in the top slot and drop 2 sizes on the pilot down to a 38 @ 1.5 turn on the air screw. I have the slightest stumble now and is only noticeable street riding getting up to speed or maintaining around the 1/4 throttle area. If I only used it as a woods bike I would never know there was an issue.

Seems like this is a characteristic of this bike the more I research the more I see people having similar issues not running smooth or 4 stroking in the same area I am.

I have a BGQ needle on the way and hope it clears up the little hiccup I have let.

Overall its 95% better than it was

Thank you for the follow up. I'm glad to hear you've got it running better.

Yes. Thank you for the follow up. A follow up post can help someone in the future.

Good to hear!