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I just rebuilt the top end in my 1987 kdx 200. I have gotten through the break in rides and yesterday started to open it up some. From 1/8 to 1/4 throttle there is kind of a stutter/stumble then past that it goes strong, getting into the power band. I am guessing it is some sort of carb/jetting problem. I am running a B9ES plug which I think is a colder plug than some of you use. Any direction on where I should start to address the problem would be appreciated. Thanks.

How old is your pilot jet?
They can get cruddy and pitted and screw things up. Or if someone cleaned it improperly in the past.
Check or replace that first and see

Most of us run a B8 plug. That shouldn't have much effect on your low end stumble though. Make sure your pilot is clean, and refer to the jetting sticky to see if your pilot is the correct size. A stutter/stumble normally makes me think it's a rich condition, where a hollow sounding bog is usually a lean spot.

Thanks guys. The pilot jet is where I will look first. I will also refer to the jetting sticky.

Julien D-Where do you ride? About the only place I have been to in WNC is Cullowhee.

Mostly brown mtn OHV, and brushy mtn motorsports. Either would probably be a good drive from asheville, but well worth it. I guess brown would be closer, and day passes there are only 5 bucks.

I have never been to Brown because people have told me it is rough and more geared to ATVs. I would like to go to Brushy Mtn pretty soon. If I get up early and go it would not be too bad of a haul for me.

gopack4749 wrote:I have never been to Brown because people have told me it is rough and more geared to ATVs. I would like to go to Brushy Mtn pretty soon. If I get up early and go it would not be too bad of a haul for me.

There is a lot of single track at brown that you couldn't even fit an ATV down, so I'm not sure I could agree with that. The main trails are double track, and open to Jeeps and ATV's, so perhaps whoever you talked to didn't get off the main trails?

The guy that maintains the trails at Cullowhee told me that Brown was for ATVs.

Today I installed a BR8ES plug with the intention of doing what Indawoods suggested in the jetting sticky. This time before I stuck the plug in I actually gapped it. I was going for a warm up ride before I started adjusting the pilot screw. Well, with the new plug-gapped at .032-I did not have any low rpm stutter. The bike ran good thru the whole rpm range. I was happy. I will mess with it later if I need to.

10-4. Glad you're happy with it. Just like to add, it's definitely worth running through that jetting process on ANY new bike you get. Be it used, abused, or brand freshy new off the dealer floor. The OEM's have to jet rich, so that people don't buy a bike and then ride it at high elevation and blow it up due to a lean condition. Just something to think about. Running good is well and good. Perfectly jetted makes a world of difference!

I agree, I do need to jet it correctly. It would probably run that much better. I guess it would really scare me then!