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98 KX 125, stumbles if you get on the throttle too hard from a low RPM

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Hey there everyone,

So a friend of mine purchased a 1998 Kawasaki KX125 today, and it's a pretty good bike! It treats him good, and overall seems to do the trick, but it does have one nasty habit I can't quite understand.

First off, it was having idle issues and a funky bog off of idle. Definitely a bit too rich and causing some wierdness. Dropping down a pilot jet size got it idleing like a charm and it felt great. Unfortunately, it's still not quite perfect.

If you let it sit for half a second and idle, and then grab a bunch of throttle, you can completely kill the engine. It dies just like a four stroke with a bad accelerator pump would. Infact, if you're riding around at a very low RPM, and twist quickly on the throttle, the bike will just barely pull at all for a good long ways as barely chugs along.

Soooo... any ideas? The bike has a Keihin PWK airstriker carb in there if that is important to know. It's got a 40 pilot jet and a 168 main jet. Needle position and shape unknown, presumably OEM.

Perhaps it's the reeds?

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Awww, nobody?

Setting the idle high helped take care of the problem, and given that you ride a two stroke on the pipe all the time anyways it never shows up. I wonder what it's about...

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Awww, nobody?

Setting the idle high helped take care of the problem, and given that you ride a two stroke on the pipe all the time anyways it never shows up. I wonder what it's about...

Broken reed petals most likely.

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Sounds like a lean on the bottom bog. Put a 42 pilot in there with a 158 main jet. Set the needle clip on the 4th position from the top.

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125's don't pull large throttle opening from lugging rpm very well. However, your low rpm bog does sound like it's lean.

I had a 99 KX125, all stock. I was running a 42-45 pilot and 155 main at ~3,000 feet elevation and temps in the 70-100F range.

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