Is this a jetting problem?

[Woodbyrd]

I have a new to me 97 KDX220. It has a knarly pipe with a gold silencer. It also has Boyesen carbon reeds with the following jetting; 142 main, 38 pilot, stock needle with the clip second from the top. The riding is typically 500 to 1000 feet above sea level with a temp of about 80C. If the bike is sitting on stand the throttle response is fast and crisp but tends to backfire slightly when throttle is chopped. When running in first gear is never seems to clean up, almost bogging. From second on up it pulls cleanly and fast. I am unsure what to change to get first to pull cleanly??? Is this a trait of KDXs or is my setup wrong?

Thanks for any help

 

[G. Gearloose]

suspect your air screw is out too far for that small pilot. start 3/4 - 1 turn out and make small 1/16 turn adjustments.
If still not satisfactory, next step may be to check the reeds for cracking. Either way, ping back the FMF model number (k 30/35) and if your airbox lid is modified yet, so 220 owners can advise.

 

[Woodbyrd]

I was told it was a gold silencer, I see no markings on it other than a 7-65( on the bracket that mounts to the bike) and a FMF sitcker. Yes the airbox lid has been removed.

 

[woods_rider1]

I know its hot in Alabama, but not that hot. 80C = 176F No wonder your bike runs like crap :p

 

[Brian]

Does the backfiring sometimes happen when coasting or decellerating?

 

[Woodbyrd]

Stan,
Yes it backfires when I am decellerating. I have messed with the air screw like Gearloose recommended and no luck. I dropped the pilot also to 35 and it made no difference. I now am beginning to wonder if the neddle has been worn down causing it to run rich or if the float value is faulty.

 

[Woodbyrd]

I just remember and it may help. I rode a hare scramble today, my first, and I only got 24 miles of mostly 1st and 2nd gear riding before I had to go on reserve.

 

[Brian]

Woodbyrd, mine does the same thing. Sometimes it sounds more like knocking, other times like pinging. Mine also does this when in neutral, and I rev it slightly, and as goes back down to idle, it knocks or backfires 1-3 times, but is very inconsistent, sometimes more, sometimes less, but it does rarely return to idle with no odd noises.

 

[goldman15]

I have a very similar problem. However, my bike has decent throttle response but in 1st, 2nd, 3rd gear when I get past 1/4 to 1/2 throttle there is no top end or in other words the engine just makes this gurgling(don't know if I spelled this right) noise not a high rev sound. In the upper gears it will stay on the pipe as much as a KDX is capable of I guess. This is not the KIPS valves they work fine. Jetting is completely stock as is the rest of the bike. Where should I start with my jetting. I would like to start with the most conservative approach. Thanks for the help!

 

[Woodbyrd]

Goldman15,
I am unsure what your problem is. I am just a novice at this but I would check your reeds and compression. It might just need the top end rebuilt and cleaned. You can find some good articles on this on Eric Gorr's and JustKDX's web pages. Also do a search in how-to forums and see what you come up with. Also get a service manual, this will help you visualize the parts everyone is talking about.

 

[Brian]

Woodbyrd,
I'm considering doing a top end job next, as I've checked timing and jetting, and think it might be piston slap? You're bike has the same symptoms as mine, so I have another question. Is the knocking or backfiring noise worde when you're bike has just been started? Mine is. It makes much more noise when cold than when warmed-up, but still is noisy after warming up. Is you'rs like this also?

 

[Woodbyrd]

Stan_Flemmings
No, mine acts just the same when it is warm or it is cold. There is really no change. I ordered a new needle and choke today. I also need to check my float level again. I might have over looked something. I will let you know if this solves the problem because it could solve yours also.
What is your compression at right now?

 

[Brian]

I'm not sure what the compression is, but I know it's OK, because it has plenty of resistance when you slowly kick it over. Why did you order a new needle and choke? I haven't checked the float bowl setting, but the way I understand, If it's too high, it flows out of the overflow, if too low, runs lean, anywhere in between is fine, right? Don't hesitate to post anything you find. Have you checked you're ignition timing? What are symptoms of worn/chipped reeds? I haven't checked mine, but would that even be a factor?

 

[Woodbyrd]

You can buy the tool to test the compression cheap (around 30) and then you would know for sure. Why I ordered the needle is because it seems worn around the tip and may be letting to much fuel through. The choke because it is worn out and I am afaid that it may be stuck partially open causing it to run rich on the low end. These are just straws but I have checked everything else that I know of. As far as the float goes I just know that it makes it impossible to jet correctly if out of specs. I am going to try to make some head way on the float part.
The ignition is still stock and I have not messed with it. I will look into it but I do not think that it can go wrong unless played with.
The reeds very much could be part of the problem, they control the flow of air into the carb. If the air flow is not consistant or predictable then the ridding experience is less enjoyable. I.E. the jetting is not right. How long has it been since the reeds have been changed? Take a look at them and see if you see any gaps or frayed ends.
I am over my head in this but I do know that if I do it once then I will know how to do it again. There is alot of info here, THERE IS AN ANSWER!

 

[Robcolo]

"Not cleaning up" and "bogging" are two completely different situations. The first is due to a rich fuel setting and the latter is due to too lean a fuel setting.
Seeing the jet numbers that you reported, I'd guess you are too lean on all of your jets & needle position for your altitude. We run larger jets here in Colorado @ 5000+ feet.

 

[kdxtaz]

But did you see his mileage? 25 mi's & hit reserve. Larger jets won't help that!
I have a similar problem with my 200 - Can't clean up the bottom even with a 38 pilot. Air screw seems to have no effect and I always hit reserve at around 25 mi's. Choke looks ok, new top end, new reeds, new jets, & new needle. I'm about to buy a new carb, but would hate to spend $200 with no results. Sorry I'm no help, but I hope you figure this out 'cause I think we're in the same boat. BTW - in spite of this, my bike runs excellent. :silly:

 

[Brian]

kdxtaz, does you're bike make the noises described here? Woodbyrd, do you think that worn reeds would have an effect or be related to the knocking? What octane are you using? I use 93 pump gas. Reeds are probably stock, and have never been replaced.

 

[kdxtaz]

Stan_Flemmings:
Mine does not make the pinging/ knocking sound that you describe, nor does it backfire on decelleration. The backfire may be from a lean condition, but how could Woodbyrd's be lean and eat that much gas? The pinging/knocking may be piston slap, especially since it does it worse when it's cold. When the piston heats up, I'm sure it expands taking up excessive clearance? I'd do that top end and check the main bearing side clearance while you're in there. The only probs mine has is the hopelessly rich pilot circuit and bad gas mileage.

 

[Brian]

I'm leaning more towards piston slap the more I read. My bike runs clean everywhere, but is just noisy. I wonder if a new top end would help? Or is the cyclinder slightly too large from the factory?

 

[Woodbyrd]

This is what I am wondering how can I be lean and burn so much gas? As to "bogging" or "not cleaning up" I would have to say that it is "not cleaning up". After I try the new chock and needle then I am at the end of the rope and will have to take it to a real mechanic. KDXTAZ, I am sad to see that there is no answer right now.
Stan
I run 92 also but I have to agree with KDXTAZ that if you do a top end job and maybe the reeds you will have some luck. You may even do some research on changing your heat rating on your plug. I am unsure of the post but Rich Rohrich talked about chosing the right plug.

 

[Woodbyrd]

Stan_Flemmings
Along with the top end job you might need to have your cylinder redone with NiCom. As far as the cylinder being to large from the factory, I doubt it. It probably just needs some loving, remember it is a 97.

 

[Brian]

Maybe it would give me an excuse to get it bored to a 225 :p

 

[Woodbyrd]

Right now I just want mine to run good on the low end. My riding is all in the trees where this bike is designed to excell. If you do it I want to hear how much better it is.

 

[kdxtaz]

Woodbyrd-
Please keep us posted on your progress & results.

 

[Brian]

I'll be doing a top end soon. I'm pretty sure now that it's piston slap, or a rod knock. I'll post results as soon as I can :)