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I have been trying to figure an issue out with my kdx220r for about 4 months. It suddenly runs and sounds rough.... When I ride the bike at a more moderate pace it doesn’t tend to display any running problems. If I am quicker on the throttle and ride it hard (like I want to ride it) in more open areas it eventually starts to run terrible and the exhaust note changes drastically. It always seems to happen after I really get on the pipe hard and get off it, then it’s just kinda stuck running bad for the rest of my ride. The idle also gets higher when warmed up but it begins dip down very low and comes back up high unless i give it a little bit of gas. I am at a loss on what could be causing it. I had a thought.... clearly I like to use high cylinder pressures when I ride it because I like to use all of the power. It seems the longer I sustain higher cylinder pressures the problem begins. I wonder if I am dealing with detonation. My 220 has all the frp mods with all the RB mods.

sounds like you may have a fuel delivery issue. Have you verified your petcock filters are clean? Carb is clean and jetted properly? Next step after that would be a leakdown test, but if it runs fine without opening it up I'd look at fuel delivery first. have you looked at your plug to see if it looks lean?

Definitely sounds like fuel issues, make sure fuel tank cap breather is on the right way and working correctly and petcock filters are clean

bufftester wrote: ↑02:14 pm Sep 26 2022 sounds like you may have a fuel delivery issue. Have you verified your petcock filters are clean? Carb is clean and jetted properly? Next step after that would be a leakdown test, but if it runs fine without opening it up I'd look at fuel delivery first. have you looked at your plug to see if it looks lean?

The bolts just spin when I try to inspect it. It did flow consistently when I have drain it in the past. I do actually remember cleaning out the tank real well and shaking it around and hearing something loose inside. I flipped it over and something fell out but I never cared. Thanks

DonnyV wrote: ↑03:12 pm Sep 26 2022 Definitely sounds like fuel issues, make sure fuel tank cap breather is on the right way and working correctly and petcock filters are clean

I can blow through the breather. Definitely gonna check the filter thanks

I’m very worried about the fact that it’s idling down very low when it’s warmed up. It’s like it has 2 different idle speeds, one low rpm idlee that’s barely hanging on unless I give it more throttle, and another pretty much normal idle. Gonna try a new float valve.

It does sound like the float valve could be a problem. Sticking open it’s rich, sticking closed it’s lean. I recently ran into this on my bike. It would idle real low if I leaned the bike to the left and real high if I leaned it to the right. I noticed it because on the kickstand it would idle way down. Also when I was riding it would either have a real low or real high idle and would change by the minute it seemed. It had me stumped and the guys here said to check the float valve and that fixed it. Also polish the seat and barrel like in this video. On our carbs you polish it while it’s in the carb, don’t try and remove the needle seat, then spray it out and blow some air through it.

When you heard something fall out of the tank that was probably your petcock filter. If your petcock screws just spin and you can’t remove it you should run an inline filter.

John_S wrote: ↑04:14 am Sep 27 2022 It does sound like the float valve could be a problem. Sticking open it’s rich, sticking closed it’s lean. I recently ran into this on my bike. It would idle real low if I leaned the bike to the left and real high if I leaned it to the right. I noticed it because on the kickstand it would idle way down. Also when I was riding it would either have a real low or real high idle and would change by the minute it seemed. It had me stumped and the guys here said to check the float valve and that fixed it. Also polish the seat and barrel like in this video. On our carbs you polish it while it’s in the carb, don’t try and remove the needle seat, then spray it out and blow some air through it.

When you heard something fall out of the tank that was probably your petcock filter. If your petcock screws just spin and you can’t remove it you should run an inline filter.

I’m going to give this a try for sure. I should mention it has done this with both carbs I have. One frp 36mm I had originally and the RB carb. I did swap out the same float valve for each carb though. My plan is to use a new float needle valve with a freshly polished seat. New one are cheap so Ill put on a new petcock somehow. Also going to throw on a new ignition coil and see what happens.

John_S wrote: ↑04:14 am Sep 27 2022 It does sound like the float valve could be a problem. Sticking open it’s rich, sticking closed it’s lean. I recently ran into this on my bike. It would idle real low if I leaned the bike to the left and real high if I leaned it to the right. I noticed it because on the kickstand it would idle way down. Also when I was riding it would either have a real low or real high idle and would change by the minute it seemed. It had me stumped and the guys here said to check the float valve and that fixed it. Also polish the seat and barrel like in this video. On our carbs you polish it while it’s in the carb, don’t try and remove the needle seat, then spray it out and blow some air through it.

When you heard something fall out of the tank that was probably your petcock filter. If your petcock screws just spin and you can’t remove it you should run an inline filter.

I noticed recently when taking the expansion pipe off it came out of the cylinder very easy. It goes in very easy as well. The o rings are pretty fresh from a few months ago. Couldn’t be making the best seal but I never see a lot of spooge coming out of it. Do you think that might be a possible cause. And what can I do to insure it’s sealed up nicely with the loose fit? I have heard of using rtv but I kinda wish there was something I could wrap around the neck of the expansion pipe then pop it in.Thanks

I've used high temp RTV sealer for years on the exhaust. It's easier than dealing with the o-rings IMO.

SS109 wrote: ↑11:14 pm Sep 28 2022 I've used high temp RTV sealer for years on the exhaust. It's easier than dealing with the o-rings IMO.

That’s what I’ll do. Do you think this can cause it to run like it does? Thanks

It can let some air in, which would cause it to go lean, but it's pretty rare. of course, you've tried so much it's worth a shot!

Eliminate as many possibilities as you can.

You should look into a temp gauge. There are ones that splice into your coolant hose and have a little digital readout mounted remotely where you want it. Jetted good mine is in the 170’s on flowy 3rd and 4th gear trails, 180’s on slower trails, and 190’s even the occasional 200 on slow sections with hillclimbs and not much air passing over the radiator.
Be nice to know whether it’s real hot when it’s acting up. My radiator cap wasn’t doing its job and the bike would get to 200+ quick. I didn’t notice it boiling over either, I replaced because of the quick rise in temperature and it was an instant fix. It was back in the 170’s on the same loop.
I’d say none of our 20 year old radiator caps are worth keeping.

John_S wrote: ↑08:34 pm Sep 29 2022 You should look into a temp gauge. There are ones that splice into your coolant hose and have a little digital readout mounted remotely where you want it. Jetted good mine is in the 170’s on flowy 3rd and 4th gear trails, 180’s on slower trails, and 190’s even the occasional 200 on slow sections with hillclimbs and not much air passing over the radiator.
Be nice to know whether it’s real hot when it’s acting up. My radiator cap wasn’t doing its job and the bike would get to 200+ quick. I didn’t notice it boiling over either, I replaced because of the quick rise in temperature and it was an instant fix. It was back in the 170’s on the same loop.
I’d say none of our 20 year old radiator caps are worth keeping.

Hey. I have tried all the previous suggestions and it’s running awesome. Sealed my exhaust using rtv, polished seat and new float needle. Took it for an hour ride and it didn’t act up once. I have just one issue where the idle eventually drops down after sitting or it’s just hanging, not sure which. Not sure how to post videos on here I’ll try to figure it out so I can show what I mean. Thanks

In the video, is the engine fully warmed up? Sounds a lot better than a few posts back! :-)

KDXGarage wrote: ↑03:16 am Oct 11 2022 In the video, is the engine fully warmed up? Sounds a lot better than a few posts back! :-)

It was nice to finally get my riding fix in without it acting up. Yes, it was fully warmed up. I made a make shift fuel level gauge with a tube and a holed drilled in a spare floatbowl cap to visually inspect the fuel level. The fuel level was definitely over 2mm above the mating surface for the bowl. I’m thinking the fuel level may be a bit high causing the idle to eventually drop but not sure yet.

Well, it is a two-stroke, not a car, so it won't idle forever. :-) Clear it out if needing to idle for long. It sounds pretty good to me.

KDXGarage wrote: ↑10:53 am Oct 11 2022 Well, it is a two-stroke, not a car, so it won't idle forever. :-) Clear it out if needing to idle for long. It sounds pretty good to me.

Very true. Hoping she stays consistent for my next ride. I plan to get some GoPro footage soon.