Kehin PWM 38mm

ericlachance · Apr 5, 2003

Hi, I just recently bought a 1996 yz250 that is equiped with a 38 mm Kehin PWM carb. When I got it home, of course my freinds came over to see it... One of them played around with the choke lever. I didn't think anything of this until I noticed it said idle adjust on the bottom part of it. It also says open on the choke knob with to arrows pointing to one side... I was wondering if turning the choke knob to one side or an other has any effect on the idle speed or on the air fuel mixture.

Thanks eric

cr25096er · Apr 5, 2003

yes the choke know controls that idle speed.

ericlachance · Apr 5, 2003

so what your saying is that, by turning the choke knob either vay, that changes my idle speed? wich way is wich? I know this sounds stupid, I should turn it while the engine is running and listen for the changes in rpm, But I havent started it yet because it's not jetted for the cold weather we are experiencing right now(-10 celcius).

Eric

atc3434` · Apr 6, 2003

Good call on not starting the bike in such extreme cold. When you do get warm enough weather, do crank it up, and let it warm up fully. Then yea, just turn that choke to see which way ups the idle, and which way lowers it. Between that and the air screw, you should be able to find a nice steady idle. Dont' buy into that 2 strokes don't idle crap either, cause they certainly do, quite well if adjusted properly! :) Congrats on the new bike!

Rcannon · Apr 6, 2003

You can make that carb idle, or you can make it have excellent throttle response. You cannot have both.
I chased a maor jetting problem on mine when I first bought the bike. There was a dead spot on the bottom end that refused to go away. It finally went away when the idle was set low enough for the bike to fun for only 10-15 seconds when the throttle was closed.

This is no problem at all while riding. Somewhat of a pain when warming the bike up, but that is why its so easy to adjust.

SuperLooper · Apr 6, 2003

On my 88 cr500 the book calls for the idle/choke adjustment to be turned out approx. 6 turns from bottom. You might check for your bike, if not set properly the bike will be hard to start.

atc3434` · Apr 6, 2003

Hmm.... I think I'll try backing my idle back just for kicks, to look for any change in throttle response. Its amazing already though, no flat spots, and decent idle. Be a fun test though. What kind of bike are you working with there, Rcannon?

Rcannon · Apr 6, 2003

I have a 1997 YZ 250. Different bike but the same carb. I think you might be surprised.

The difference is not staggering, but that annoying little stumble went away on mine.

atc3434` · Apr 6, 2003

Huh, cool. I'll check it out on my Mikuni. I can't imagine getting better respond than I am now, jettting it top notch, but its a fun, easy experiement.

Rcannon · Apr 6, 2003

I know it sounds nuts. I think the idle circuit an dthe pilot jet are closely related. I believe a too high idle screws up this relationship.

The same thing happened on a KX 65 I was playing with.

Lorin · Apr 7, 2003

I agree. At the very least, turn the idle down when jetting your bike. If you feel the need to crank it up after that, your choice. I dont feel the need to have a bike idle for more than a few seconds, especially at the possible expense of jetting.

atc3434` · Apr 7, 2003

I think I see what ya'll are getting at. Your not meaning NO idle, per-say, but more of a low, it'll quite eventually idle. Thats the way my YZ is now, it'll idle in and out of gear, but extemely low, and occasionally might quit. I'm not sure how long it will idle on its own, I usually am blipping the throttle anyways. Haven't had a chance to try bringing it lower yet, but later this week, after the snow storms give up!

Kehin PWM 38mm

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