jsirvine's bike Q's go <here!>

[canyncarvr]

But...an 'H' kdx 200 with a 140? That doesn't sound even close. Granted, no-one call tell you how to jet thru the web (or on the phone or any other way), but I don't see a 140 in the 200 with the environs you list.

Granted, no bike is just the same as some other, but I run a 150/52 depending on temps at elevations to 6000'. A 140 is a l-o-n-g way from that. And with a top clip? That means #1 I presume...the slot closest to the top of the needle? When I run a -74L 'up there' (a 39.95mm needle), it's on clip-5! (with a -30 pipe)

Start a new thread...maybe restate your question? Things like, 'I'm at 4000', ran at 500' and it was fine...' are unclear. I assume you dropped a '0'..but, why assume anything?

Give it another shot. ;)

p.s.
How's that, mr. whorton? ;)

 

[JasonWho]

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[jirvine]

I know I have much to learn on jetting. I have 2 KDX200's. Mine has a PC pipe, KN filter. I got it slightly used, all stock. It would foul plugs and load up quickly on low throttle. I managed to lean it way out and it seems to run very well now. Nice throtle response, might use a little more on top. No mre plug or loading up problems. The other KDX, lowered for my daughter, also a 2000, was used and somewhat roughly at that. It came supposedly set up for high elevation but I think it had a 158 and maybe a 42 pilot. It always had abrupt throttle, open it up fully and it would take a couple seconds of slowly winding up before it hit. But it never fouled anything. I ride at 4000'-5000' and occasionally ride at 9000. I started to lower the main and seemed to get it somewhat better but the problem was still there. We then rode both at about 600' in more humid conditions and it had been cured. So I figured lower elevation runs great, when I get back home at 4000'+ I needed to lean it out. So it is down to 140 (stock pipe and airbox) and I moved the clip up but that didn't cure it. Also smokes like a pig compared to my better running one. Otherwise runs fine, is this a jetting problem or something else? This past weekend I had both bikes up to 9000', mine ran fine although perhaps weaker as it should but the bog on my daughters was there. It ran fine if you kept the revs up but that's not how a KDX should be is it. Any suggestions welcome. This weekend I can play with it. Do I need different needles?

 

[G. Gearloose]

Originally posted by jirvine
stock [snip] airbox

This causes the jetting to be too rpm-dependent.

The bog is a lean condition, until the revs come up then excessive airbox vacuum richens the 140 main's effect into the realm of acceptable A/f ratio.

Fix the airbox first,and throw in a bigger (150 +) main before riding it afterward else risk damage.

Set the main to optimize WOT performace only. Don't fiddle with it to 'fix' symtoms at other throttle openings.

Then set needle, pilot and AS to make it tractor for her.

 

[canyncarvr]

What he said.

A 140 isn't right....and neither is the 158.

Although some do it differently (fluffy bunnies though they be), one method of jetting has you set the main first, as g-loose says...@ WOT (either by 'feel' if you know what you're feeling for, or by air/fuel mixture ring...read THIS . Pay close attention to the pics).

There are some other good threads on the same subject...here's ANOTHER.

RR's comment regarding heat range (page 2) is likely one of the most important bits of information you'll come across hereabouts.

A needle will be mostly responsible for your bike's 'personality.' You can make it a hard-hitting front-wheel-off-the-ground all the time ride, or a smooth, even nicey-nice ride (good for that 70+ mile hare scramble in the muck).

Don't gloss over this stuff. While I can take a lot of space and use too many words to get the job sensibly done...g-loose told you everything you need to know in a couple of sentences.

 

[CaptainObvious]

You said at 600' the bike felt like "it had been cured" and when you got back to normal (for you) altitude it felt sluggish again.

Another thing to keep in mind: bcause of the reduced air density at 8,000' your motor can only produce 75% power, regardless of jetting. There is simply less air to mix. Correct jetting will improve throttle response, but it will never get you your lost horsepower.

 

[jsirvine]

Originally posted by G. Gearloose



The bog is a lean condition, until the revs come up then excessive airbox vacuum richens the 140 main's effect into the realm of acceptable A/f ratio.


If the bog is lean then why did the bog disappear when I ran at 4000' lower? If lower elevation = more air/leaner mix. Essentially didn't I lean it out by riding at a lower elevation and at which time it ran fine. I assumed (right or wrong) that my bog at 4000+ was a rich bog so I leaned it further. And last weekend at 9000' it ran worse again. My other KDX ran basically fine at all of those elevations, of course weaker at 9000 (so I took the 500 off the trailer to cure that).

 

[G. Gearloose]

Originally posted by jsirvine
If the bog is lean then why did the bog disappear when I ran at 4000' lower?

Because for a given rpm, thicker air will cause more delta-P within a restricted airbox, pulling more fuel from the same venturi than that occurs with thinner air.

Similarly, at low altitude, the main circuit will richen sooner (read: lower rpm) than at high altitude, thus giving the appearance you observed, the symtom improving at low altitude.

in summary, you will fight this to fustration (if your not there already) until you remedy the airbox. It has been documented for years now that it is an essential first step to dialing these bikes.

 

[jsirvine]

Originally posted by G. Gearloose


in summary, you will fight this to fustration (if your not there already) until you remedy the airbox. It has beed documented for years now that it is an essential first step to dialing these bikes.

What does remedy the airbox mean? The problem has existed with the stock airbox, I took it off when at 9000' last week to see if that would help. I've been cleaning up a few other items on the bike but now I'll go warm it up and see what happens with some richer jets in it.

 

[jirvine]

So I plated with it some enough to annoy a neighbor.. I'm at 4200', have a 40 pilot which I didn't touch. I think the stock is a 42. I have the lid to the airbox off and a uni filter, little dirty. Stcok exhaust. Started by playing with the AS just getting it idling higher. I had a 140 main and started working up from there. I think it seemed to run best, less low rpm bog (slow winding up and then hitting) with the 155. My clip was on the highest, #1 so I dropped it to #3 to see what difference that made. Not much really, now have the AS 1 turn out. The bog is still there although less than last week. Don't know what the next step would be? Should I go back to the 42 pilot? Or?? Thanks

 

[G. Gearloose]

Uh, stock is 48. This suggests you havn't fully digested the years of similar queries to yours, nor the cornicopia of info HERE , or perhaps the FAQ, so dig in..! ;)

For now, Set your needle for best half-throttle performance.

155 is likely a little fat at your altitude. Set with a WOT plug-chop first.

Don't set the AS for highest idle, its the best way to dial in a bog. Its just too lean off idle.

Set the the AS for best off-idle torque,:
Most use the idle-in 2nd gear -slightly-uphill-lugging off-idle roll-on method.
I'm partial to the the ' stopped, first-gear off-idle let-the-front-end-climb-a-rock ease & stall-resistance method.

A 40 pilot is often too skinny with a large diameter stock needle. I suspect the 42 is in order; yes even at your altitude.
Also check that the 40 is not partially blocked.

If the needle is stock, it is set fat at #3, even if you were at 50'.
So reply with the numbers stamped on the needle to verify it is what we think it is.