Not Just for the KDX . . .

Questions and Answers about the best carb and Head mods available for the KDX.
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Indawoods
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Post by Indawoods »

The Powervalve is disabled on Kirsten's and it's a stump puller.
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fuzzy
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Post by fuzzy »

Cool! Wasn't sure if you did that while re-assembling or not! How does it get on the pipe now? I'm sure the pipe stilll has great top-end effect...
'91 KDX 200 Project $300 KDX
'95 KDX 200 Project $600 KDX
'94 WR 250 Always a project
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Indawoods
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Post by Indawoods »

The bike runs great... just keeps pulling and pulling.... still hits.... just not as abrupt.
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Jeb
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Post by Jeb »

Disabled - shut or open?

It's easy enough to try the powervalve adjustments - I can actually do it while it's running. It even has little indentations or "clicks" - just loosen the cap enough to spin it in little discrete movements. The last time I fooled with it it opens at around 6-7k or so, I actually did that so it opened when it was less effective if you can believe that. When I first bought the bike it opened at lower RPMs and with the needle a notch richer it came on pretty hard.

But all that's changed and I've gotten used to it, so I'm gonna go a few clicks-at-a-time more slack and see what happens. I'm hoping it does more what like Inda's saying.

What does Kirsten ride anyway?

A BTW - Cometic or Boyesen makes a spacer (for some bikes) that you install under the resonance chamber cover to give the chamber more volume. You guys ever try that on your KDX, like maybe cut several gaskets from some thick material kind-of-thing? A few of the Gassers rave about the nice effect on low end on their 200s. Just a thought.
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Indawoods
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Post by Indawoods »

Kirsten rides a 94 KDX 200 and the claw is not on the KIPS actuating rod. It may open on it's own but I doubt it. I can't move it by hand.
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"People ate cows a thousand years ago for the same reason we eat them now. Cause they are easy to catch.We're not savages,we're just lazy. A cheetah could taste like chocolate heroin. But will never know. Those bastards are fast!!! "
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canyncarvr
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Post by canyncarvr »

That (re-sizing the Hemholtz resonator) has been fussed with on the KDX. I never read that anyone that tried it thought well of it.

Never tried it myself.

..there's some useless anecdotal 'I heard..' info for 'ya!

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Using a perceived level of knowledge to boost my self worth.
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Jeb
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Post by Jeb »

Worth mentioning . . .

put 4 hours in at a place called Eagle Creek. LOTS of lugging about, the only time I was in first gear was if I had to get off the bike and walk it. Much of the trail was in third.

This time, however, got a different needle - replaced the stock N8RH with an N3EJ. Here's the profile compared to the last ride:

Image

All of the data sets other than the baseline (N8RH) represent the N3EJ so there's only one curve off of baseline. Same PJ, MJ, slightly higher temperature. Note how the needle runs lean up 'till about 3/8 throttle then gets a tad rich over the stock needle.

My take on the results:

-Off idle throttle response is SUPERB.
-Cleaned up the rich burbling when you roll open the throttle easy.
-Responds quite vigorously and quickly to wacking the throttle opening.

Today was the warmest riding to date - high 60s, low 70s ish, so the air is thinner. But . . . noted little spooge on rear fender or S/A. I didn't get ANY spooge out of the powervalve drain tubes. Need to continue to monitor this . . . and I didn't get a chance to hold her open for a long period of time to "blow" the gunk out. Still have the same S/A packing on my last trip.

Still got tinkering to do.

One last comment. 5 of us rode: myself, two youngsters, and two good riders (from my point of view anyway). The best rider was a guy in his 50s, he's rides a KTM XC450 and he's something else of a rider in addition to being a heck of a guy and a big help. He made a comment to me, some constructive criticism you see, about how I'm not spinning the tire enough for a two-stroke.

I didn't have the heart to tell him that I was running a gear higher than he probably thought!!
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Jeb
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Post by Jeb »

A little more follow up - yesterday afternoon I finally got to tinkering with the carb settings and the powervalve. Starting really trying to dial in the A/S, made a few changes. Then I started to ease up on the powervalve. Eased back on the tension of the powervalve spring a couple of clicks at a time and took little rides to see the effect. After a couple of tweaks I noticed something feeling like it wanted to kick in, almost like a hitch or something. So I started making fine adjustments with the A/S.

At about 1+1/8 turns out I got quite an eye opener. If I roll the throttle smoothly it's rather well-behaved, pulls nice and strong, doesn't get out of hand. The low end, the really low end, is quite smooth and steady. But the first time I get the revs up just a little and snap the throttle . . . KABOOM, that little hitch before becomes an EXPLOSION. Always had the hit, but I've NEVER felt it quite like that before, scared the daylights out of me!! The good news you have to dig the spurs into the thing by yanking open the throttle after the flywheel has managed to get a little momentum. I was able to replicate this in 3rd easily, no clutch whatsover, with my butt up on the front part of the seat and my knees tucked into the rad guards, the front wheel rares up REALLY EASILY.

Not a good setting for slippery conditions, must remember that.

And I got some of the powervalve drip back.

Got a PC pipe coming so I'll be changing things around again.
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Post by Jeb »

One more posting for good measure and to sort of complete my input for the RB mods on a 250 mx'er.

I noticed during a harescramble that the bike seemed tired on the low end and it worried me a bit. Still had lots of spit, though, but just not where it seemed to before. Since that race I've installed a slightly used PC Platinum pipe. My first thought was that this wasn't going to work. Low end seemed diminished then it kicked in at mid range - violently. Oh no, wrong pipe. But then I went back to that powervalve and realized that somehow it had unwound while I was adjusting. Set it at a tension to delay the valve opening for higher RPMs only. THERE IT IS! Outstanding low end, enough grunt to catch you off guard if you're not careful.

Fuzzy is exactly right, at least for these kinds of bikes. Whatever is causing it: the enlargement of the exhaust port, the resonance chamber closing off, or both, you don't want it at low RPMs. It made the 250 run like my kiddo's 65 and that's freakin' downright scary, old school 2-stroke big bore hit.

I tweaked just a bit more by relaxing the tension on the spring - a little - to get the powervalve to open just above midrange (approx). As you reduce tension on the spring you can't feel the powervalve opening until you get to about midrange. Any lower and you feel the power flattening out and then it comes on. VERY interesting, very tuneable.

The PC Platinum on a bike like this with Ron's mods is a HOME RUN for our kind of riding with some jetting and powervalve tweaking. You can tune it for NO hit, just solid power. Like a KDX on steroids. I'll bet a Gnarly pipe has a brutal low end . . . in fact I'm banking on it and I can't help but eventually go for one of those too!

Anyway, just wanted to wrap this up for anyone considering Ron's mods for a 250 mxer. It seems reasonable that the same results could be had on a relatively recent model KX, YZ, etc.

And I'm once again a very satisfied customer.
"No farmer ever plowed a field by turning it over in his mind" -George E. Woodbury

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