Why Won't This Carb Work???

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Why Won't This Carb Work???

Postby jafo » 06:48 pm Dec 02 2004

I have an '84 KDX200 and bought a used Mikuni carb off an '87 KDX200. I put it on my bike and it idled great but had no power and sounded like it had a miss in the engine when I gave it gas. It's almost identical to my original carb. The differences are the slides, slide needle, and the position of the choke and the idle screw is on the opposite side. I tried puting the jets out of the old carb into the newer one but it got worse, would'nt idle, and fell flat when giving it gas. I was going to try to exchange the needles but the needle in my old carb is much fatter and longer than in the newer carb so it would'nt fit the new carbs slide. I've looked at the plug and it looked brand new after trying the new carb, not a spot of carbon. What could I be overlooking?

Why change the carb? The old one has a crack in the idle jet circuit. It's below the jet though. It's cracked on the part that extends down into the fuel bowl. The old carb works good, it turns the porcaline a gold to tan color shade. It turns the grounding part of the plug, the part right above the threads by the grounding strap, almost a blu-ish brown color. Like it got alittle to hot. I notice a detonation sound when the engine is at hig RPM's. I run hi- octane fuel, around 91 octane.

Jon.
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Postby Jason » 07:00 pm Dec 02 2004

Does the crack in the original carb affect how it runs?? Did you try a larger main jet?

Maybe you could call Jeff Fredette at http://www.frpoffroad.com to see if he has a used '84 carb. That or the usual, eBay, http://www.ebay.com.

Since the original carb is a VM32SS, you could also try to find another VM32SS and see if it will work, using your original jets. Look for other early 80's bikes, like Yamaha YZ125 or IT175 / 200, maybe real early 80's KX125.
Thank you, Julien D for all your hard work!

PLEASE! Do not "dip" PWK Keihin carbs in Berryman's to clean them! It will damage the internal o-ring (jet block gasket).
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Postby jafo » 06:24 pm Dec 03 2004

Thats what I'm trying to find out, if this crack is affecting anything. I don't know how it would have gotten cracked in that spot anyways.

It had a 320 main jet, I went all the way up to a 350 jet. Still no change.

Where do you locate the carb number on the carb.? I'd like to just see what carb this is for sure.

jon.
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Postby Jason » 09:16 pm Dec 03 2004

I am not sure if there is a model number on it. I was just quoting from the Clymer manual. The stock main jet in a 1984 carb is a 260, according to the Clymer manual, clip postion 3 on the needle clip, 40 pilot jet.

Any chance you can take a picture of the original carb? Maybe the original carb is not an original carb and someone had already swapped it out.
Thank you, Julien D for all your hard work!

PLEASE! Do not "dip" PWK Keihin carbs in Berryman's to clean them! It will damage the internal o-ring (jet block gasket).
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