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I've noticed that despite adjusting the idle screw, my KDX's idle has a tendency to creep up if left unchecked. I have to hit the choke from time to time to get the idle to come back down. Can anyone tell me what might be the problem and how to fix it? See the video below which I captured about 30 minutes ago.

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An air leak leaning it out?

How is the power while your riding?

When it gets to a point will it stop increasing RPMs?

Are any of the vents clogged?

I assume you have cleaned the carb.

Carb was cleaned a month ago. I'm thinking air leak myself. The rubber intake manifold has a lot of surface cracks; not sure if they've gone all the way through but I assume at least a few have. The previous owner had some black sticky gunk coating the manifold. I took the gunk off and now that I think about it, idle was fine before. Perhaps the PO coated the manifold with whatever that stuff was to stop the leak.

As for power while riding; feels a bit rough up to 1/4 throttle. Past 1/4 to WOT, the bike pulls fine and hard. Also, the idle will stop increasing after a certain point - I think.

I ordered a new intake manifold from RMATV. It's on back order till mid November.

Someone on here used plstidip on on and if I remember right it worked well. Might be worth a try until the new one comes in.

rbates9 wrote:Someone on here used plstidip on on and if I remember right it worked well. Might be worth a try until the new one comes in.

This stuff?


I'll give it a try. I hope it's fuel resistant.

That might be about the same stuff. It is meant for tool handels so it should take a little gas.

The other guy that did it was doing a rebuild on air cooled bike so that might help find the post.

My buddy used stuff called Seal All on the carb boots of his old motorcycle and that fixed his air leak issues.
From what I have read sealing up the cracks is actually a pretty solid fix and will last a long time.

Thrahl wrote:My buddy used stuff called Seal All on the carb boots of his old motorcycle and that fixed his air leak issues.
From what I have read sealing up the cracks is actually a pretty solid fix and will last a long time.

Thanks for the suggestion. WIll look into that stuff as well.

BTW, since this thread was about idle speed I was wondering if you guys set your idle by ear? I prefer a fairly slow idle - something similar to what the bike sounded like in the video when I applied the choke. It may be too slow for some. I don't recall seeing anything specific about a preferred idle range in the service manual though.

Ive fixed one with plastidip before, you have to dremel down into the bigger cracks or it will just crack there again. I used the dip kind not the spray and just applied several coats with a putty knife until the dug out areas were even with the rest. It doesn't come out real smooth this way but if you wanted you could sand down any high spots once its dry and use the spray. Oh and you need to sand the boot and clean it with brake cleaner or acetone beforehand. I did this at the beginning of the summer and it still looks good.

Thanks for the suggestion. WIll look into that stuff as well.

BTW, since this thread was about idle speed I was wondering if you guys set your idle by ear? I prefer a fairly slow idle - something similar to what the bike sounded like in the video when I applied the choke. It may be too slow for some. I don't recall seeing anything specific about a preferred idle range in the service manual though.

I like mine set just above stalling RPM. The bike can sit and idle by itself for maybe 10-15 seconds and then I have to give it a little blip. I don't really ever let it idle that long though.
Some people believe that a 2 stroke shouldn't be able to idle for more than a few seconds before needing a blip. For my slow paced woods/field riding though that is just a hassle.

Thanks for all the replies.

I went to Lowes today before everything got locked down due to the hurricane. I picked up a can of Plasti-dip. So far so good; just waiting for everything to cure. I tried stuffing as much as I could into the bigger cracks but they still appear if you flex the boot a little. Hopefully this will hold me over until I get a replacement intake manifold. The original one I have is right at the end of its service life.

Just wanted to follow up and let you guys know that the plast-dip method worked well. Idle seems to be quite stable now. Thanks again for the tip.

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