Does removing the jet block equal death?

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Brian
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Does removing the jet block equal death?

Post by Brian »

I can't seem to keep my KDX 220 (with RB head and carb) running clean at part throttle openings. When I got the carb and head done several years ago, I had a #42 pilot and CEK needle. The bike ran pretty good. I went to a DEK needle and the bike ran even better. Over time I noticed the bike started to run blubbery below 1/4 throttle. I went to a #40 pilot and that helped for a while then the blubber came back. I went to a #38 and eventually a #35 pilot. Each time I went smaller on the pilot jet the bike ran much cleaner at about the 1/8 throttle position but a little worse (lean) above 1/2 throttle. Now the bike is getting real blubbery at about 1/8-1/4 throttle again.

I have tried to change the needle clip position and going to a larger main jet, and changing the float level. I've turned the air screw in and out, from 0-5 turns out. I've changed the reeds and even installed the V-Force 3 reeds. No matter what I do the bike runs too rich just off idle and too lean above 1/2 throttle.

My other two KDX's have stock carb's and they have very consistant jetting, and run much cleaner at the 1/8 throttle opening.

I'm wondering if the gasket between the jet block and carb body might be deteriorating. I'm not sure how to get a new one if I take the jet block out of the carb.

Any ideas?
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Does removing the jet block equal death?

Post by KDXGarage »

The o-ring is available from a few different places.

Have you tried a thicker needle? On my 1994 with stock carb, going to a thicker needle cleared up some 1/8 - 1/4 throttle richness for me.
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Does removing the jet block equal death?

Post by rbates9 »

I have been chasing around about the same issue with the RB carb. :hmm:
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Does removing the jet block equal death?

Post by Brian »

I briefly tried a DEL needle which is a "thicker" needle. All that did was make the bike so lean the only thing it could do was idle or full throttle. I'm afraid to try a smaller pilot than the #35 I have in it now. I was thinking of getting a needle with more taper to it so it's richer above 1/2 throttle but I feel like I'm chasing a ghost.
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Does removing the jet block equal death?

Post by Brian »

I removed the jet block from the carb body when I got home from work this morning and I found some stuff that kinda looks like sealant partially plugging two of the three holes that are between the jet block and carb body. I can't tell if it actually is sealant or if the o-ring/gasket is coming apart. The rubbery stuff was still attached to the o-ring/gasket. It reminded me of someone using RTV to repair a damaged gasket and it gets squeezed out a little when the parts are put together.

I'm not sure if that would make it run rich and blubbery at 1/8 throttle but it was restricting the passage from the air screw to the pilot jet. I'm wondering if the deteriorating o-ring/gasket could be allowing extra fuel to seep into the low speed circut. That seems more likely to me because I have been stepping down the pilot jet and it runs better for a while and then starts getting blubbery again.
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Does removing the jet block equal death?

Post by Brian »

I have a new jet block o-ring/gasket on the way from Jets R us but in the mean time I put the carb back together and went for a ride. It's the RB carb with DEK needle, 4th clip down from top, #35 pilot and #152 main. It still seems to be too rich at about 1/8 throttle and too lean above 1/2 throttle. If you roll the throttle on all the way and let it build up some speed (power valve open) and roll the throttle back, just off full, it actually accelerates harder. That tells me the main is too lean. If you let the bike run slower with the throttle at about 1/8, it seems real blubbery, no matter what I do with the air screw. All the airscrew seems to do is affect the throttle responsiveness, not how it runs at a steady speed.

If I put a bigger pilot jet in it, like a #42, all the other carb problems seem to fade away but then it runs really lousy below 1/4 throttle and it seems to load up real bad when you run at part throttle.

I'm hoping that the new o-ring/gasket will help but in case it doesn't, anyone got any ideas?

Do you guys know what RB cuts the slide to? it still has #5 stamped on it.
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Does removing the jet block equal death?

Post by canyncarvr »

Brian wrote: Do you guys know what RB cuts the slide to? it still has #5 stamped on it.

Uh...asked on the 10th and not answered? Shame on you guys! :naughty:



He used to cut them to a 7. The OEM stamp will still be there, but additionally, you will see a letter stamped close to it. If it's a 'G'..that's a 7mm cut (count by letters).

You reference getting the head and carb 'done'. Does that mean your carb was modified? Specifically, you are running a modified OEM carb, or you have a 4-vent AS?
If you roll the throttle on all the way and let it build up some speed (power valve open) and roll the throttle back, just off full, it actually accelerates harder. That tells me the main is too lean.
Not to open another worm can, but A/F mix at WOT is best checked with a plug-chop.


Describe the orientation of your reed block to the cylinder. That question moreso fits the OEM reeds, but maybe you took the MotoTassinari's out?
I've turned the air screw in and out, from 0-5 turns out.
Try the SSS (Super Sweet Spot). It's there...and it's easy to miss. 2 1/2 turns out for your baseline, adjusting by no more than one indicator width to either side (a reference to using RB's finger-adjustable screw) followed by at least a few minutes of riding under moderate load conditions. Although it's easy to miss, when you find it, you will immediately know it.

Yes, I don't have a 220. Other 220 riders have reported similar results having found the SSS as 2-hunny riders have, though.

If you had the jet block out, you probably (hopefully) already did this...but do chase the pilot circuit holes: A musical instrument string (ex: guitar) works well.

Yet another use for a G-String.....I mean, besides being a hat.

Good luck!!

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Does removing the jet block equal death?

Post by rbates9 »

The infamous CC! Welcome back!
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Does removing the jet block equal death?

Post by Brian »

Does removing the jet block equal death?

by canyncarvr » 02:33 pm Jun 15 2012



Brian wrote:Do you guys know what RB cuts the slide to? it still has #5 stamped on it.



Uh...asked on the 10th and not answered? Shame on you guys!

I'm honored sir and let me say, welcome back!

While chasing this carb problem I have changed Reeds from stock to Boysen 607's and finally got the Moto Tassarini reeds and block, just to eliminate the reeds and block as the likely culprit (and it was an excuse to get the Moto Tassarini reeds :mrgreen: ).

I realize the plug chop is the most accurate way to determine main jet size. I'm just illustrating that in trying to clean up part throttle operation it's effecting full throttle operation.

It's possible that this is just the way the RB carb is. If I return to the standard recommended jetting for the RB carb (#150, DEK 4th, #42, 2 1/2 turns) the bike runs great in every manner except below 1/4 throttle (at steady speed, not loaded like when going up an incline). I didn't even notice it untill I rode my other (stock) KDX back to back. It's just annoying to be cruzing along with a slower rider, or on a level section of trail under a light load and my bike is coughing and loading up. Then when I get a chance to "get on it", it hesitates and needs to "clear it's throat" before running clean. By going to a smaller and smaller pilot jet, the part throttle blubber is nearly gone but I've traded that for a 1/2 throttle and above "lean out" at low engine speeds.

I was thinking a needle with more taper (EEL) might help but the Jets R Us web site wouldn't let me order one. I also realize that by making so many changes I may be causing my own problems.

I have two other stock carburated KDX's, another 220 and a 200. I'm thinking I might swap carbs around and see if the problem follows the carb or the bike.

I did get my jet block o-ring/gasket (3 of em) but have not installed a new one yet. Also, I did chase out the holes in the carb while the jet block was out. I have some copper "break away" wire. It looks like safety wire but it's so soft you can break it with your hands so it won't scratch.

P.S. Modified stock carb.
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Does removing the jet block equal death?

Post by KDXGarage »

Welcome back, welcome back, welcome back. :grin:

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Does removing the jet block equal death?

Post by Julien D »

canyncarvr wrote:
Brian wrote: Do you guys know what RB cuts the slide to? it still has #5 stamped on it.

Uh...asked on the 10th and not answered? Shame on you guys! :naughty:

And this is what we need you for!

Good to hear from you!
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Does removing the jet block equal death?

Post by canyncarvr »

I realize the plug chop is the most accurate way to determine main jet size. I'm just illustrating that in trying to clean up part throttle operation it's effecting full throttle operation.
Understood.
I was thinking a needle with more taper (EEL) might help but the Jets R Us web site wouldn't let me order one.
I recall trying an EEK once. Didn't work for me (meaning: Your Mileage May Vary, No Warranties Expressed Or Implied, No Animals Were Harmed During The Filming Of This Reply, Etc.). That steep of a slope has a very late-starting taper. The transition from part-to-mid throttle was poor.

It's just annoying to be cruzing along with a slower rider, or on a level section of trail under a light load and my bike is coughing and loading up.
You are not talking about a 'happy' 2T skippy note, right?
Then when I get a chance to "get on it", it hesitates and needs to "clear it's throat" before running clean.
That later statement would preclude the happy-skippy part...but...I'm asking anyway to be sure I unnerstan.


I can't say how my bike runs at a 'normal' air-screw setting (1 1/2 or less). It's been too long since my carb's been there. BUT it does seem there were some response issues I wasn't happy with at that setting.

Find the SSS. The RB-modified carb does have a modified low-speed air circuit. That's why there's an SSS to find in the first place.

And (imo) why the 'normal' setting of the air-screw doesn't work in the second place.

Re: Carb swapping.

I would expect you will find the 'problem' follows the carb.

At this point, though, I don't know there's a problem to start with (other than some adjustment).


My bike is 'happy-skippy' most of the time. I like it. It tells me nothing is too tight. But, throttle response is instant, too.

FTR...I'm running a red-top JD needle on clip -4, and something like 42-150 with a 'rev' FmF pipe.

My bike ran similarly (the yippee-skippy part) with a DEK-4, too. I am running an AirStriker RB-modified carb (another FTR).


If I understand the question correctly, there IS something out-of-whack. Keep after it..you'll get it.


Any chance the compression is low?

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Does removing the jet block equal death?

Post by Brian »

I installed the stock 33mm carb I "borrowed" from my wife's KDX 220 last night. When I get a chance this afternoon I'll take her for a ride and see if the blubbery 1/8 throttle follows the carb or the bike.

It's sure interesting to see the stock 33mm carb side by side with the RB modded carb. The RB carb sure is pretty in the inside compared to stock. All polished and stuff.

While my RB carb is off I'm gonna replace the jet block o-ring/gasket.
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Does removing the jet block equal death?

Post by canyncarvr »

Just to cover one particular base...

The result of the cable retainer NOT being in the slot of the needle nut is similar to your description of your bike's operation.....

You don't have to be a mech wizard to miss that. I know 'cuz I'm not and I have. :oops:

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Does removing the jet block equal death?

Post by Brian »

Ok, I just went for a very short ride with my "borrowed" stock 33 mm carb and it actually seemed to run about the same at around 1/8 throttle as the RB carb. Maybe even slightly worse (more blubbery). The stock carb was actually more responsive above 1/2 throttle than my RB carb. That may be because I'm so lean on the pilot(#35) of my RB carb.

I'm going to put my RB carb back on with a bigger pilot jet, maybe a #40, and see what I get.

Is it likely that, aside from a possible leaking crank seal, the differences I'm noticing between my RB modded bike and my stock bike(s) is the pipe? I have the desert (rev) pipe on my 220, my wife's 220 has a stock carb with the woods pipe, and my son's is a totally stock 2006 KDX 200.
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Does removing the jet block equal death?

Post by Brian »

I replaced the jet block o-ring/gasket on my RB'd carb and put it back on my bike and went for a ride today. I upped the pilot jet to a #40 (from the #35). It seems to run better above 1/4 throttle and is more responsive than when I had the #35 pilot in it but it is still really blubbery at about 1/8 throttle. I have the air screw out about 3 1/2 turns now. Still tuning it but I just can't get rid of the blubbery feeling. It seems to get worse as the bike warms up.

I was looking at the stock PWK 33 and the RB carb and slide side by side (I took pictures but don't know how to post). I noticed that the RB carb has a slot cut into the jet block where the needle goes into it. I was wondering if that could be related to some of the issues I'm having. Could that slot be why the air screw has little affect at idle but changes the responsiveness when whacking the throttle open?
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Re: Does removing the jet block equal death?

Post by Julien D »

After a certain amount of distance out, the air screw will no longer affect idle but will affect throttle response. That's true for any 2t carb.
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Does removing the jet block equal death?

Post by Brian »

I installed a new jet block o-ring/gasket and put my RB modded carb back on my 220 with a larger (up from #35) #40 pilot jet and the DEK on 4th clip down. The bike feels better above 1/2 throttle but is way burbly at about 1/8 throttle and it tends to load up if cruising at part throttle for more that a few seconds.

I then changed the main from a #150 to a #152 and put the DEK on the 5th clip position and put a smaller #38 pilot jet in it and it ran much better everywhere. The burble at about 1/8 throttle is less and the bike runs crisper. I have been messing with the air screw and it seems to run best about 2 1/2 turns out. In or out any more and it starts to run much worse at 1/8 throttle.

I'm going to install a #155 main and put a #35 pilot and leave the DEK at the 5th clip position and see how she runs.
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Does removing the jet block equal death?

Post by Brian »

So right now I have a #155 main, #35 pilot and DEK 5th clip down and I'm liking it. It seems to run much much cleaner (and leaner) at part throttle openings with the smaller pilot and the #155 main seems to help with the lean feeling around 3/4 throttle. I'm not sure how far out the air screw is right now. I was adjusting it by feel while riding so I'll have to actually count how many turns out it is.

All these jetting changes are really changing the personality of my 220. It runs really crisp now, almost motocross, snappy power. I think it will be harder to ride in really slow, slippery conditions but it is much more perky and responsive in faster conditions. My oldest son who used to ride an RM 125 says my KDX feels more snappy than my other two KDX's. My other KDX's are much better for my younger son and my wife to ride. They are much much mellower.

I haven't had the chance to ride my KDX in slow, slopy conditions since making the jetting changes so I don't know if the crisp snappyness will be a worth while trade for the comfortable mellowness it had, even though it had the RB mods to the head and carb.
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Re: Does removing the jet block equal death?

Post by zepplin153 »

wow. This is very helpful. I am having similar problems, and have done many of the same things. right now its running pretty good but I am getting the same low end rpm symptom. I have one other that I have never had until the most recent change. I get a little Pop when letting off throttle. it gives a slight instant of power too. It is really noticeable when coasting downhill. any ideas?
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