KDXRIDER.NET

Recently I have been getting my bike to run much better with the experimentation of different needles and jets.

My question is that even when jetted well, will the KDX experience a bog somewhere in the power range?

For example, I have cut my slide to a ballpark 7. 38 pilot, 150 main. With a CCL needle in the 2nd clip, I can whack it open as fast as I can in second gear from 3mph and the bike jumps and goes. Air screw is 2/3 out here.

But if I am moving slightly faster and have the throttle open just a tid bit, like 1/16th to 1/8th, then roll it on a bit slower I get a quick bog. More like it cuts out for a millisecond or two, then goes. I played with the airscrew and tried different needles like the DEK, CCM, BEM, DGJ, EEL, etc. and I can get the bike to run great everywhere except for this little spot.


Quick snap open, as fast as I can move my wrist, no bog, bike goes, front end comes up. Very slow to medium roll on, smooth crisp acceleration, wheel lofts nicely and controlled. From 1/16 steady throttle,I get the dreaded bog then snap of power, medium roll on here. Not a crackle, definitely a bog, more like a "Waa..waaAAAPP!!"

The only thing I can think of is that I cut the slide more than a "7" and went too lean on it, causing the bog in the 1/16 to 1/8th range. A smaller diameter needle than a xxL loads up at idle and decel, and a larger diameter than an xxM produces a large long drawn out unridable bog all over the place. If I run the 40 pilot the motor loads up in the low end. If I set the pilot out enough so the motor doesn't load up, the bog worsens. Also, if I have the air screw less than 1/2 out, it will load up with the 38 pilot. Any thoughts? I wish I had Ron cut my slide, now I'm just guessing.

Other factors: 93 Pump gas Yamalube 2R 32:1, sea level 80* F, 20 hours on bike from new, Boyesen 607 reeds, Pro circuit plat 2, Clean air filter BR7ES plug, no airbox lid at all. Later in the summer, I will save enough to go with the RB mods including the head mod on my 200.

WoW!! maybe more ride time and less tinkering should be in order.

From what others have said, I'd put the airbox lid back on w/ holes drilled in it. Sounds like you're 99% there though.

1) Put the air box lid back on and try it again.
2) Go 1 step richer on the Main jet and try it again.

You are talking about the performance of the carb at WOT (even if the RPMs are in the bottom end of the power band). If you richen things slightly on the main jet you'll be able to lean things slightly on the pilot circuit (or slide for that matter) and get rid of the hesitation/hiccup-and-go problem. The air box lid was the ultimate solution for my hesitation situation. I couldn't jet it away without being ridiculously rich in all of the other carb circuits. The DEK or DEL has a richer tip than the CCL. This would also be a help slightly richening things at WOT.

That's a lean bog you discribe alright. Usually just fixed with moving the clip down one position on the needle. Otherwise, check you CDI and sparkplug. Start with a fresh thin-wire plug and see if that helps at all.

It's not so much a particular carb circuit that can be a problem, but the transition between them. The slower throttle opening accentuates those transitions as opposed to !bang!-WOT.

Some things to ponder:

Try some 40:1..see what improves...or not. By changing the premix ratio you are changing the air/fuel ratio across the board as opposed to changing circuit by circuit (different throttle ranges).

The same idea applies to the airbox lid.

To each his own and all that...but I do agree with Rhodester. I had a lot better result from a ventilated lid than with no lid. To tell the truth, I didn't spend the time on it I probably should have. While it may not make sense from a performance standpoint I didn't want the noise of no-lid, so I eschewed the (possible?) performance gain.

The 152 idea is good, too. Florida and a 150 I doubt is correct.

Something to keep in mind. A #7 slide works with RBs modified carb. I don't know that it works with an OEM carb. It's easy to say, 'Your slide is too lean for an OEM carb body,' but I have no facts to support that.

...doesn't mean it isn't so!!

A very big part of Mr. Black's modification is the work he does
on the pilot circuit. BTW, his ideas come from cutting carbs up see what's inside and years of dyno testing. It's not a matter of, 'Hey! I think I'll drill this hole out!! Bigger is better, right??' I'm saying that if Ron puts a #7 slide with the rest of his work on the PWK, I would NOT assume that means a #7 is good without the rest of his work.

re: 'A smaller diameter needle than a xxL loads up at idle and decel'

This is a part of what makes me wonder about the stock carb body and the #7...and think that there is a mismatch. You should not have that loadup problem with a 'K' diameter unless you are using a small taper º (like an 'A') which puts the taper start pretty high up on the needle (close to the clip end..taper starts too soon).

Also something to keep in mind..if you buy a new slide..the PWK in the KDX is a bit weird. Rhodester pointed this out recently...it's been noted before but is rarely an issue. If you BUY a new slide for your KDX PWK, get an airstriker slide. Well...to be exact, I know I bought two slides for my PWK, got something that didn't fit both times, before I gave up on the idea. I recall Ron saying something about this a few years back..and I'd bet that Rhodester is correct. I have not bought an airstriker slide and put it in a KDX PWK body.

...I put my PWK slide in my airstriker, though!!

Sorry...in an effort to be exact about particulars...things may get hard to follow when I'm talkin'....

BTW...regarding Boyesen power reeds:

Boyesen wrote: Top reed opens at lower RPMs allowing for more air and fuel flow giving you better throttle response
Bottom reed opens at higher RPMs for maximum flow

Sorry. But I don't think much of that idea. What is the thinking in cutting off 1/2 the airflow in the reed cage to improve anything? What on earth does that do to rarification and smoothing the airflow? It sounds like something thought up in the break room one day. BOOOooooo!!!

You know CC, I was thinking about the reed idea. I had a major problem with the Boyesens in the past with the KDX, I put them in with the stock pipe, 152 main, 40 pilot, R1174K on the second clip. Bike started on the first kick cold, but wouldn't run for do-do. It blubbered, knocked and farted until it fouled a plug 10 minutes later. I pulled the reeds out and changed NOTHING and the bike ran fine again. I made sure the reeds and plastic cage were installed correctly too.

Like my above post stated, I do have the full set of 607's in now, but I could not really tell a difference over the stockers. Matter of fact, I thought the stockers were more crisp (Flame suit on... .)


How about this breakroom idea > I will try the reeds with the stockers on one side of the cage and the boyesens on the other! Mix and match! The best of three worlds!!







You guys will laugh, I had an old 34mm PJ carb laying around and set it up for the KDX. Man with a DGQ-3 150 main 38 pilot, #6 slide, that thing cooked on the bottom end and midrange. Top wasn't so good. But the bottom/mid was electric like a 50cc scooter/trials bike. Changing the carb out only took 10 min. I changed it back because the PWK is the better carb, it made more overall seat of the pants power. The PJ was damn electric though.....

Yeah, I'm starting to beleive more and more that a small carb is the ticket for woods work. I can always sacrifce the top-end. Even when my 250 is anemic on the top-end it will still spank the pants off of most bikes...

How about the best of four worlds??

...you could glue those reeds onto a radvalve body!!