Bike has no "top end power"

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barncat
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Bike has no "top end power"

Post by barncat »

I went out last night and noticed bike seemed "flat" when at W.O.T.

Took it over to my buddies house(he's a 2-stroker) He road it, and thought the same. He said bike should be tearing it up. I have tons of low-end, the KIPS is working(can here the rattle) but even in neutral, with W.O.T. it goes flat.

I have a Mikuni carb, with open element. Stock pipe. Not sure of the reeds.

I thought jets, buddy thought reeds. he wasn't sure if this bike was new enough to have Carbon Fiber reeds, but guessed that, maybe it should have fiberglass instead.

Bike runs great in the low ranges, but lacking the upper limit.
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fuzzy
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Post by fuzzy »

What year is the bike to have a Mikuni on it? 86/7?
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barncat
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Post by barncat »

1991 KDX200
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Post by dfeckel »

Is this a new development? Was it running well up until last night?

It really sounds like the powervalves could be the problem.

When I rebuilt the motor for my hybrid, I had what sounds like the same problem. Great low end, but flat in the mid and non-existant on the top. It turns out that I forgot a little pin to locate the actuator shaft, so the valves weren't opening.

If you have an E series, it could be because of broken valves. They could also be gummed up to the point where they won't open, either. The E has a plastic gear which spins the PV governor under the inner clutch cover. I've heard tell that they can strip. If so, then your PVs wouldn't open.

I'm not sure if you can do this with an H series, but with the E, you can remove the actuator arm cover (you first have to pull the pipe), and also take off the resonator cover on the left side of the cylinder. Before you put the pipe back on, try rotating the actuator arm to cycle the power valves. Look into the exhaust port to see if the valves are moving in unison. If so, put the pipe back on and start the bike. Rev it up to where the PVs should open. You should see the actuator arm move in an attempt to open the valves. If it doesn't, you may have a problem inside the governor assembly under the inner clutch cover. If it moves properly, check on the left side of the cylinder to double check if the left valve is in fact opening and closing with the actuator (you can see the left valve open and close with the resonator cover off).

If all this checks out, then the powervalves are probably okay.
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Post by barncat »

Well, I just picked the bike up a few weeks ago. The problem is intermittent. I can twist the throttle a couple times and "clear it out", and it will run fine. This is why I was thinking fuel/air.
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Post by KarlP »

That sounds like a sticky KIPS or jetting off
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Indawoods
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Post by Indawoods »

Ditch that Mikuni!
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Post by barncat »

What is the recommended replacement? I noticed it wasn't OEM

The other thing I need to address is the fact that the petcock leaks. It seems to be coming out of the back basket area.

Without going into great detAil then, the fact that I can hear the KIPS, isn't the end all be all of operation.
I have done some reading on it, but am still learning.

Thanks for the info so far.
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Post by Indawoods »

35mm Keihin PWK

It could very well be all a carburation issue....
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Post by barncat »

Thanks boss. I'll see if I cant dig one up.
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Post by Indawoods »

I think there is still one for sale on this site....

*EDIT* Yup... if it's not gone yet! Get the entire throttle assembly if you can... no problems then...

http://kdxrider.net/forums/viewtopic.php?t=9293
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"People ate cows a thousand years ago for the same reason we eat them now. Cause they are easy to catch.We're not savages,we're just lazy. A cheetah could taste like chocolate heroin. But will never know. Those bastards are fast!!! "
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Post by barncat »

Thanks again. I went to pull the Mikuni off, and the throttle plate at the top, has some boogered up screws.

Figures all 3 of my bikes need some sort of work...
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Post by Julien D »

Still could be kips too. Just because they rattle in an E series doesn't mean the gears on the subvalves are stripped. you can verify by pulling off the pipe, and the small plastic cover on the RH side of the cylinder. Pull the kips rod by hand and observe the main valve and two sub valves through the exhaust port.

Agree on ditching the mikuni. We tried for quite some time to get a mikuni set up for the 91 kdx. Eventually we gave up on it.
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