pilot or needle to cure off-idle richness?

[D36-108A]

I had a bunch of fun on my 200 yesterday but its carburetion felt a little fat when I'd crack open the throttle. Especially noticeable when I'm in a higher gear below the meat of the powerband. It rips when it's on the pipe.

I'm not sure if this is best remedied by the pilot jet or needle position (yeah, yeah, I know, both, plus slide and needle shape, but let's keep it simple). Should I go to the next leaner pilot or lower the needle a notch?

FYI, 96 200, K-35, RAD, 50/50 pump/race, 155 main, 45 pilot

 

[jboomer]

I'd suggest dropping the needle one notch. This is a simple, cost effective (read $0 -- easy on the wallet) way to at least rule out one of your two possibilities. What's the worst that could happen? You'd end up having to raise the needle back to its original position while you're installing your new pilot!

 

[Matt90GT]

have you played with the air screw?

adjust that. If you are more than between 1.5-2.5 turns out from full in, you need to adjust the pilot accordingly. That will give you a sign that the pilot is at fault, and very easily. Otherwise mess with the needle.

 

[canyncarvr]

Starting from a condition of spot on jetting, and now it's different, the lower temps of winter probably are wanting a richer pilot.

But...45/155 is quite a bit on the rich side..like a LOT on the rich side. For pump gas. Race fuel maybe changed that. There's a whole lot more to race fuel (brand, makeup, intended use, etc etc) than just adding 'race fuel'. Jetting would certainly depend on the makeup of that fuel.

On the 'keep it simple' side, I'd certainly spend some time on the air screw. My bike can turn from 'bummer' to 'w-o-w!' with 1/16-1/8 turn of the air screw. That's even in the 3rd gear uphill pull in the 3/8-3/4 throttle range...which fits with, '..a higher gear below the meat of the powerband.'

Don't discount that iddy-biddy screw. It makes a night and day difference in throttle ranges higher than you'd expect.

 

[D36-108A]

I checked the airscrew, it was only 1.5 turns out when my notebook indicated I had been running it at 1.75 or 2.0 turns. Anybody had that thing slip? Maybe I bumped it going for the choke knob.

 

[MX175]

Hey... make sure you are adjusting the airscrew and not the idle screw. The airscrew is a little slotted screw that is almost hidden in the carb body. You can't bump it when you are going for the choke. The idle screw is the big honker hanging off the left side and sets the position of the slide when your hand is off the throttle. Set the airscrew for max. rpm and then set your rpm with the idle screw.

 

[WoodsRider]

Hmmm, I ran the same jeting in my KDX. I think I had the 1174 needle with the clip in the #2 (from the top) groove. Off-idle was always rich, but dropping down to a 42 made it too lean. It would bog just off-idle if the air screw was more than 1/4-turn out. I never did try the 1173 needle.

 

[D36-108A]

Yeah I know the difference MX175. It just turns real easy and it was strange that it was off from its previous setting. I've set the airscrew for the highest idle speed a long time ago, but I'd rather set it for best off-idle throttle response if it will help.

WoodsRider, the 1173 needle is leaner right? I think that's my next step after the AS and pilot. Looking through my notebook, I had a bunch of off-idle issues noted at various races. According to some other resources, it seems the straight portion of the needle contributes a lot to off-idle response.

 

[WoodsRider]

I'm pretty sure that's the one. CDave would know for sure. It's been over two years since I owned my KDX. Mine had all the FRP mods with a KG-30 pipe and TCII silencer. The 155/45 combo was a good baseline for jetting. I only had to change the main in winter or summer. Should've tried the leaner needle, but never got around to it.

 

[G. Gearloose]

Setting the airscrew to highest idle is the best way to dial in an off idle-bog. (read lean)

1173 needle is richer off idle than the 1174..

Perhaps what you think is rich,might be lean...

Yes, the air screw should be set for best off-dle responce; changing needles or pilots before you do that would be unproductive.

 

[canyncarvr]

Hi idle is the starting point for the AS/pilot circuit. Best response will likely be 'in' (richer) from there.

The comment: 'I've set the airscrew for the highest idle speed a long time ago, but I'd rather set it for best off-idle throttle response if it will help.' indicates you're at the former right now?

It's not a 'set it and forget it' sort of thing. You'll find yourself tweaking it for temp and elevation changes. 10-15º and/or a couple thousand feet of el. and your bike will benefit from an adjustment. Not NECessary ..but it will run better if you do.

You might consider a different needle profile altogether. Something in a 'C' (1.5º) perhaps. The CEL has gotten good reviews.

 

[D36-108A]

I adjusted the airscrew for highest idle speed once or twice but I haven't fiddled with it at every ride or event. Maybe I should.

If I can't get it crisp and I want to try a different needle, what's a CEL? I thought I had an R1173K or R1174K (whatever's stock).

Indeed I have considered I'm wrong in diagnosing the off-idle flat spot as rich. I have experienced various rich conditions on various bikes, but few lean conditions. I'm kind of guesstimating it as rich based on my other experiences and the fact that I'm a little on the rich side elsewhere, based on plug/piston color and better general performance in colder weather and worse in warmer.

 

[G. Gearloose]

I, and I'm sure others can appreciate the 'rich everwhere' observation tainting the off-idle presumtion that it must be rich there also...
To better describe the 'air screw too open' symtom, it WON't sound like a needle bog (bwwwaaaww); it feels more like a little delay or knotchyness off idle, just a touch flat, then zap, the rear is breaking loose, prone to stalling in the roots and rocks when going easy, making the technical sections that much harder, because you have to factor that delay into your technique. The stock needles have a large diameter straight section so you don't get much gas off that circuit until the slide goes up further, so..

When the air screw is optimized for off-idle torque (yes it will be on the rich side), you will have more progressive and consistant power delivery off idle, making log hopping and and similar tasks easier; it will just plain tractor through the rough..

 

[Jim Crenca]

My 2 cents:

* My bike doesn't respond nearly as well to A/S adjustments as CC, although it definitely shows improvement when tweeked for temp, altitude, etc.
* My bike needs a MUCH richer main than most (as rich as a 165 depending) but also likes a 38 pilot
* I think you can do better than the stock needle; you might want to check the archived thread (in archives section) for about a million technical ideas from some pretty sharp tuners

 

[D36-108A]

Gearloose, you've described my off-idle flat spot exactly; maybe it is lean. I'm going to dial in the air screw at Clear Creek next weekend and if that doesn't do the trick I'll look into a needle.

Jim, 165/38 is freakish.

 

[D36-108A]

Update: I rode at Clear Creek today, first loop throttle response was poor, felt fat. Wouldn't wheelie in third, wasn't crisp. Poor power climbing hills in third. Turned the screw out a quarter turn, to 2.5 out (!). Next loop (slightly warmer out) it was worse, almost blubbery. Went a quarter turn in from the original position and got my throttle response back. Picks up the front wheel everywhere without the hesitation, has better, cleaner power on the bottom. Still not perfect and maybe could go another quarter turn to be even more crisp.