RB CARB Mod, What can I expect?

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canyncarvr
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Post by canyncarvr »

Changes happened over such a long period of time, I don't have any direct comparisons. Before the FRP port job, I was running 38-148. I'm putting a 38 in for this weekend. Generally things have tended toward the more lean side of things with the modifications..which indicates higher pressure differentials..which is a good thing. After all, the engine is nothing more than an air pump. The more it sucks, the better it runs.

No, that doesn't mean restricting the airflow to make it REALLY suck good would be an improvement...lest any smart alecks chime in with somesuch. :roll:

As I recall, stock slide folks (#5) had better opinions with the CEL than the CEK. But, JD (the jetting geru) does list the CEK as a desireable option for the OEM PWK. There isn't a ton of difference between 'em anyway.

It would be cool to have a sensor right at the jet block to actually SEE what was happening with air pressures. Or...an oxygen sensor with a dial-a-jet setup. Oh well......

I hadn't gotten to the C-D needle 'spearmints with my oem PWK. I'd made one change to the diameter/L1 in the oem B slope, but that was it. That ran great in Prospect (3500-7500')..got something like 80+ miles out of a tank of fuel before reserve, and that as a whole lot of hi-speed scootin' too! Nothing in the way of 1st gear grunt required.

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IdahoCharley
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Post by IdahoCharley »

Clutchcover - since we are at similar elevations- When you get the CEK you may want to try a 40PJ, 152MJ with CEK (4). Ran this on Sam's bike with the tightened head clearance, PC2 pipe and Boyseen power reeds and it worked well. The 3 clip position was a little too zingy and the 4 was more forgiving. I settled on the 3.5 as a balance between the two e-clip positions. Then when on to modify his slide to try some other needles.

Currently running JD Blue #2 with a 40 PJ and a 155 MJ. This is with a ~7 - 7.1 slide though. The DXX needles I tried seemed to overfeed the requirements of the engine in the 1/2-3/4 throttle range IMO.

The 152 MJ with a CEK and stock slide gave me a little silver edge on the spark plug electrode tip at WOT in 50 degree weather at 5000 feet. Plug color light with light-medium-brown ring at bottom of insulator. I would not want to drop down below a 150 MJ until it got to 75 degrees or so.


EDIT - Air box mods, stock silencer were on the KDX 200 mentioned above.
Last edited by IdahoCharley on 03:25 pm May 26 2005, edited 1 time in total.
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Indawoods
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Post by Indawoods »

What's your elevation Charley?
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Post by IdahoCharley »

Idaho Falls is 4700 feet. Riding starts about 5000 feet.
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Post by Indawoods »

I'm trying to get a handle on the jetting since I ride around 600' and my jetting is at 40/150 with a 7 slide, CEK needle at 3.
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Post by bradf »

Most of you guys have 2hunnies so my spearmintin on my 220 won't mean as much to you. Since it has warmed up to the mid 80's here I decided to try some low speed trail jetting test. Today I replaced the CEK-3 with a CEL-3. I left the PJ at 40, main 150. The second SS was finally found at 2 9/16ths almost 2 5/8ths. This is as far as I have ever had to go to find it. A 38 PJ at these high temps may be needed. CEL-3 was a tremendous improvement over the CEK-3 I ran last weekend. Both rides were snotty wet slippery and tight. The CEL ran very clean and best of all, the part throttle blips to loft for roots and rocks was so manageable. Plug showed a much cleaner burn too. From idle to 1/2 throttle it was consistent and smooth. I then put the DEK-3 in but it felt and sounded rich with a crackle at throttle chop to idle, and not the nice smooth snap for lofting like the CEL-3. DEK-4 was a lot to handle, way too much for fun with way too much hit. Next test will be a 38 PJ and DEK-4, 148 MJ.
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Post by dave04kdx »

I had some time to ride the bike with the new RB carb mod this evening and thought I would post my findings/opinions and also ask a couple of questions.

I did a wot plug chop and found that I was lean with the 152 Ron sent with the carb. I installed a 155 and life is good. The jetting is now 40 PJ, CEK #3, 155 main, A/S just a hair (a red one) :lol: over 2 1/2 (love that 2nd ss). Jetting is now a whole new ball game with the RB carb. The temp this evening was in the low 90's. I was running the 155 main in temps 25 degrees cooler before the carb mod.
Anyone want to give me their 2 cents worth on why this is?

CC ask a couple of days ago what I thought of the bottom end gain. After tonight I definitely think I picked up some on the bottom. Not a whopping ton of power but a smooth, responsive, manageable 4 stroke like pull. I took the bike up a hill that we call "Chicken Hill" this evening. Before the carb mod I normally had to shift into first gear about 3/4 of the way up to make it to the top. Not anymore! I did the climb three times tonight and second gear was more than adequate. :supz:

However, my bike is pinging sometimes again. This has been an on going issue and has nothing to do with the carb mod. The pinging occurs around 3/8 throttle when and goes away when I get closer to wot. It doesn't happen all the time even on the same terrain/trails. Do you guys think I have some carbon build up on the piston? I have over 300 hours on this bike I'm sure. Most of the riding has been fairly slow 1st, 2nd and some 3rd gear stuff. My jetting has been fairly close. I have used Amsoil Dominator since the bike was new. No excessive spooge and silencer packing was dry when I repacked. Any ideas would be greatly appreciated!
I am still running approx. 20% toluene in 91 octane Chevron gas.

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Indawoods
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Post by Indawoods »

Dave...have you tried tweaking the timing just a hair.... I know CC has played with this a little and may be able to help...
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dave04kdx
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Post by dave04kdx »

Inda:

I haven't messed with the timing. I have no experience with changing the timing on
the KDX. Maybe just a small change would take care of the pinging.

Dave

Edit,

I went riding this morning and the pinging seems to be heat related. Same gas, jetting only difference was lower temp and higher humididty. We had rain last night and it was around 85 degrees during my ride. Not one hint of pinging. Again the RB carb is worth the money!

Maybe the radiators cant transfer enough heat away from the coolant when it is 105 + outside?
At age 4 success is . . not peeing in your pants.
At age 12 success is . . having friends.
At age 16 success is having a drivers license.
At age 35 success is having money.
At age 50 success is . . having money.
At age 70 success is . . . having a drivers license.
At age 75 success is . having friends.
At age 80 success is . not peeing in your pants.
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