topend rebuild problems

Discussion specific to the various air-cooled KDX models sold in the USA
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Michael93
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topend rebuild problems

Post by Michael93 »

hi again everyone so finally got all my parts and redone my top end ,and first kick it started wooho but im having trouble with the carby i seem to get a sorta steady idle but i notice im getting blow back as i dont have the back boot on and the more i rev the more blow by i get whats are common causes and some fixes for thus please
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Last edited by Michael93 on 05:41 pm Jun 05 2020, edited 1 time in total.
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Re: topend rebuild problems

Post by KDXGarage »

You are running it with no carb to airbox boot (AKA, no air filtering going on??)
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Michael93
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Re: topend rebuild problems

Post by Michael93 »

i was just for start up and to check things out no riding or anything and was no wind so dust and that were near non existent, i think i may have found the problem not sure on the name but the opposite side of kips rod the cover has a crack causing a nice air leak :( after waiting since april for my new needle and only noticed it now
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Re: topend rebuild problems

Post by Wesalauzen »

So you are getting air blown back out of the carb? That could be bad reeds. The reed valve on the engine side of the carb is supposed to act as a check valve only letting air move one way when running. If air is blowing back out of the carb, I would check those to make sure they are not chipped or cracked and sit flat against the cage. I may be misunderstanding what you're seeing, but if you are getting air coming backward through the carb, I would check those first.

The cover on the opposite side of the kips rod I believe is just a closed chamber to dump the exhaust when the power valve is closed. A leak there would let exhaust gasses out, but shouldn't let anything in (if I understand its operation correctly).
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Re: topend rebuild problems

Post by KDXGarage »

on the left side (clutch) or right side?
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Re: topend rebuild problems

Post by Wesalauzen »

He mentioned the opposite side of the rod so I was assuming the left side. Correct me if I'm wrong though. Just didn't think the power valve would allow air to flow backward through the carb even if it was malfunctioning or had a cracked cover.
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Re: topend rebuild problems

Post by KDXGarage »

Yeah, I am as confused as you. :-) I was thinking backward from the carb, but now, way confused.
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Michael93
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Re: topend rebuild problems

Post by Michael93 »

Sorry guys added a pic now, and thanks for the the reply’s I’m gonna go to the my local shop and pick up some new power reeds since they have some, I also have a air leak on the boot which I will try and fix and will get back with results hopefully it’s a bit better
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Re: topend rebuild problems

Post by KDXGarage »

The cover is missing. Exhaust enters the chamber for proper power valve operation.

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Michael93
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Re: topend rebuild problems

Post by Michael93 »

KDXGarage wrote: 09:54 pm Jun 05 2020 The cover is missing. Exhaust enters the chamber for proper power valve operation.

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I have the cover but is broken but yeah broken missing same thing I guess I noticed it was broken when I had some smoke pouring out of it
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Re: topend rebuild problems

Post by KDXGarage »

Sorry to hear it.
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