RB Designs

Questions and Answers about the best carb and Head mods available for the KDX.
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skipro3
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Post by skipro3 »

It wasn't just a little crud sitting on top of the slide, it was FULL! Like in: no more could be added. I'm suprised the bike started after I cleaned the throttle cable and left the carb filled with that crap. There's a little wear on the slide and carb body, but not much.

2 clip change: I dinked with it a bit more this afternoon. Fattened up the main by one size. I could feel that!! Now when I go between clip 1 and 3 on the needle, I can feel a change. I've really enjoyed not having spooge drooling out the tailpipe but I think I'll not mind so much now that the jetting (and it's changes) make a difference where it counts, in the seat of my pants. I think the C12 I burn works better in the summer when the ambient air temps are warm than now when it's colder, hense the richer jetting required and the probable increase in spooge. More notes to be taken, saved and reviewed come summer and the bike is a blubbering around. Sure wish the bike had a thermostat that could be changed out for summer or winter temps.
BTW when you changed from the CEK to DEK did you keep the same clip position? Just want to know where to start when I start dinking with that.
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Post by BJH »

OK...Here is my lame attempt at hijacking this thread. I was wondering if pulling out the divider plate would make my RB modded carb a little more forgiving?
I want to give it a shot but I'm afraid that if it doesn't satisfy me I won't be able to get it back in. Have any of you tried pulling the plate out?
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Post by Indawoods »

I'll just trade ya!
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Post by BJH »

UH...no :wink: The bore job and circuitry work is what I needed. I'm sure of that. I would just like to know what the trade off between not having the divider plate and easier jetting would be. Or if it would even help.
I'm still a bit perplexed by the whole thing. I got rid of the dripping and gnarly exhaust that CC is refereing to but I still have a bog at the bottom. Although it is no where near like it used to be. The jetting the carb came with and I might say the same jetting that is ballpark to good for everyone else does not work with my FRP ported cylinder.
I've got it close but I can't seem to close the deal. It is rideable now and it starts ok. It is also way stronger than it was when I started stock. I actually have a top end now. Where as when it was stock it flattened out hard.
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Post by fuzzy »

BJH: Your ported cyl may require vastly different jetting....More than likely a completely different needle profile than what others on here prefer...Maybe even a leaner slide if you've got richness at the bottom that you just can't cure w/ a leaner pilot jet...

Ski: Just some FYI.....C12 is a great fuel, and as with most race fuel runs leaner than pump gas. I run it in my racing kart, and you can really take it to the gnat's butt as far as leaness and the engine will still let you know when you're pushing it. Running a 10:1 fuel/oil mix helps here too! :shock: No powervalves on those little 2-cycles...

As far as a thermostat I think you might be confusing engine temp w/ air temp? The reason jetting changes are required are to compensate to the amount of available oxygen in a given amount of air. IE higher elevation has less oxygen....Colder temps have more oxygen. The point is to adjust the jetting to work with the current air that the engine is breathing in. Now as far as a nifty device goes I would love to some sort of micro-sized air/fuel mixture guage mounted in the intake(mass air flow sensor on a car) with a bar mounted display...That would be sweet...
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Post by skipro3 »

Thanks for the info fuzzy. My concern with the air temp has to do with the evaporation of the fuel. My thought was that the cold air along with a cold motor due to the ambient air temps would prevent the fuel vaporizing as completely before ignition, thereby resulting in a lean conditon but more spooge. If the engine operating temperature was increased, then perhaps the fuel would be vaporized more completely than with cold air and a colder motor. I was thinking about possibly blocking the air flow over the radiator with a shroud or something. Like the big truckers do.
Thoughts? Opinions?
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Post by m0rie »

BJH have you tried mixing premium pump (91+) with something like C12 or Trick114? I seem to recall CC having to do a 80/20(?)mix to get his jetting right on the bottom with his FRP ported cylinder.

-Maurice
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Post by canyncarvr »

re: 'I would just like to know what the trade off between not having the divider plate and easier jetting would be.'

I surely missed something. What 'tradeoff' are you referring to?

There was talk of the air striker and its advertised 'easier jetting'.

WHAT is the correlation between that and removing the divider? None that I know of.

re: 'I was wondering if pulling out the divider plate...'

Don't do it.

For one, no, you won't get it back in. It doesn't just SIT there!

I had the plate in my oem pwk break (Ron put them in differently back then than he does now). That gave the the opportunity to experiment first hand with a quickly changed carb.. with and without a divider.

The bottom end response took a b-i-g hit..as did smoothness between low circuits.

So...besides not understanding how the two ideas got put together in the first place (eaiser jetting and plate removal), don't do it.

Oh...I did run an 80/20 pump/Trick-114 mix in an effort to get rid of some rather severe detonation I had after the FRP port job. This involves a quite long story, but the detonation was going on whilst it was throwing a good deal of spoo out the back.

Anyway, the Trick did take care of the detonation...BUT....it also pretty much WASTED the bottom end of the bike. Burned too slow.

I'm still using some..but way less than 80/20. Still 'spearminting.

BTW..BJH...What type of porting did FRP do for 'ya?...what pipe you run and how is your carb set up? Elevation? Temps?

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Post by BJH »

fuzzy wrote:BJH: Your ported cyl may require vastly different jetting....More than likely a completely different needle profile than what others on here prefer...Maybe even a leaner slide if you've got richness at the bottom that you just can't cure w/ a leaner pilot jet......
Fuzzy, The odd fact is that I'm requiring richer pilots and needles. I'm on a CEG-4 now but it seemed to like 3 better. I've been thinking of trying a DEK. My air screw likes its' setting at 1/2 out or less. It runs at 1/4 out so I guess that means a fatter pilot as well. The main looks a bit lean to me. I 'm putting pictures of my WOT chop plug in the gallery so if you or anyone else gets a chance to look at them PLEASE comment. I'm by no means a pro at reading them.
It's a bitch to start when cold and always has been even when it was stock. It takes full choke and a bit of throttle to start then has to run at idle on choke for a few minutes until it warms up. molesting the throttle at all when cold causes it to bog. After it warms up it cranks on the first kick. and runs fine less a bit of bog if I hit the throttle too fast from the bottom. A couple of quick stabs then crank it method works out fine.

42 and 1/2 out on the air screw.(Plug looks brand new at idle only)
7 slide ( Plug looks rich)
Needle@CEG-4. ( Bottom Mid- range wheelies)
Main at 155 (Plug looks lean to me see what you think)

1400 feet elevation at 50 degrees F

Jets in my arsenal box
Pilots-- 35,38,40,42,50,52,55,58, (Need 44 and or 46?)
Needles-CCJ,CCK,CEG,CEJ,CEK,CEL,DCJ,DEJ,DEG,DEK,DDK,R1173L
Mains-- 145,148,152,155,158,160,165,168,
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Post by m0rie »

42 and 45 are the pilots your missing. Also missing a 150 main.

Your pics haven't shown up in the gallery yet so I can't look at your plug chops. I'll have to check back on them later.

Have you tried the CEG-4 with a smaller pilot (40) and the air screw out around 2 - 2.5 turns?

-Maurice
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Post by BJH »

hammered it starting over
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Post by BJH »

canyncarvr wrote:re: 'I would just like to know what the trade off between not having the divider plate and easier jetting would be.'

BJH - easier control over the pilot circuit?

CC - I surely missed something. What 'tradeoff' are you referring to?

BJH - powerband change or loss in power

CC- There was talk of the air striker and its advertised 'easier jetting'.

BJH - That's what I need because I appear to suck at it

CC - WHAT is the correlation between that and removing the divider? None that I know of.

BJH - I'll take your word for it

CC - re: 'I was wondering if pulling out the divider plate...'

CC - Don't do it.

BJH - Again I'll take your word for it

CC - For one, no, you won't get it back in. It doesn't just SIT there!

BJH- That's what I was afraid of

CC - I had the plate in my oem pwk break (Ron put them in differently back then than he does now). That gave the the opportunity to experiment first hand with a quickly changed carb.. with and without a divider.
The bottom end response took a b-i-g hit..as did smoothness between low circuits.

CC - So...besides not understanding how the two ideas got put together in the first place (eaiser jetting and plate removal), don't do it.

BJH - Again I'll take your word for it

CC - Oh...I did run an 80/20 pump/Trick-114 mix in an effort to get rid of some rather severe detonation I had after the FRP port job. This involves a quite long story, but the detonation was going on whilst it was throwing a good deal of spoo out the back.

BJH - I haven' tried race gas, I'm currently using 93 octane pump gas and Yamalube.

CC - Anyway, the Trick did take care of the detonation...BUT....it also pretty much WASTED the bottom end of the bike. Burned too slow.

CC - I'm still using some..but way less than 80/20. Still 'spearminting.

CC - BTW..BJH...What type of porting did FRP do for 'ya?...what pipe you run and how is your carb set up? Elevation? Temps?
BJH - I told FRP I was fairly satisfied with the bottom end performance as it and didn't want to sacrifice any of the stock bottom. A small increase would be nice. My main concern was the flat as a pancake 220R top end.
I have a FMF Gnarly Rev pipe. 1400 ft elevation, 55F air temp, DF2 reed valve, (DF3 is on the way. I hear it helps out th ebottom end a bit more than the DF2). Carb is set up currenty at.

See my reply to Fuzzy too.

42 and 1/2 out on the air screw.(Plug looks brand new at idle only)
7 slide ( Plug looks rich)
Needle@CEG-4. ( Bottom Mid- range wheelies)
Main at 155 (Plug looks lean to me see what you think)
Plug pictures from WOT chop in th egallery.
1400 feet elevation at 50 degrees F

Jets in my arsenal box
Pilots-- 35,38,40,42,50,52,55,58, (Need 44 and or 46?)
Needles-CCJ,CCK,CEG,CEJ,CEK,CEL,DCJ,DEJ,DEG,DEK,DDK,R1173L
Mains-- 145,148,152,155,158,160,165,168
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Post by m0rie »

BJH, Those plugs look pretty rich to me.
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Post by BJH »

Anybody have pictures of proper plugs readings?
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Post by BJH »

m0rie wrote:42 and 45 are the pilots your missing. Also missing a 150 main.

Your pics haven't shown up in the gallery yet so I can't look at your plug chops. I'll have to check back on them later.

Have you tried the CEG-4 with a smaller pilot (40) and the air screw out around 2 - 2.5 turns?

-Maurice
I tried 38 pilot serious bog on thebottom. Ran OK with the choke on 40 was a bit better. 42 got a lot better. Mid clip CEG showed alarmingliny low exhaust smoke but good power. I will have to check the log book to se if your combo was run. Never did crank out the air screw that far though.
CEG-4 is where the needle is set now. I have 42 pilot it is listed there.

I'll give your reccomendations a shot next. If someone has a picture of a proper mixture ring on a plg it may help me a bit. I keep getting confliction information Light to dark tan insulator to white insulator with a 1 mm black mixture ring at the base of the insulator.
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Post by m0rie »

There was a good thread in the archives @ DRN on proper plug chops...i'll dig up a link.
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Post by m0rie »

There was a good thread in the archives @ DRN on proper plug chops...

http://www.dirtrider.net/forums3/showth ... light=plug

Was the temp and elevation consistant during all these tests?

-Maurice
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Post by fuzzy »

Yeah, as mentioned try the richer(40) pilot w/ the air screw out further. Fine air screw adjustments are pretty much mandatory every time you ride, and vast adjustments will be needed if you've changed your pilot.
Mid clip CEG showed alarmingliny low exhaust smoke but good power
Did it lean-bog at all? How did your plug look? You were probably on to something here. You're bike dosn't have to smoke like a pig to have good lubrication.
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Post by skipro3 »

m0rie wrote:BJH, Those plugs look pretty rich to me.
Me too. I put up a couple of photos in my gallery. One is rich, like yours and one is slightly rich but runs good.
Basicly, a WOT read should show the black band as if drawn on with a pencil. Yours covers 25% if the whole insulator.
I have another plug chop photo but for some reason, it keeps coming up as invalid when I try to upload it. If Inda is agreeable, I'll e-mail the photo to him and he can add it to my gallery.
You were puzzled about insulator color. If Inda gets that photo up, it will show a plug with over 100 miles on it. The black band is quite distinct and the insulator is chocolate with lots of deposits from running race gas (lead).
A plug chop should always start with a new plug. The insulator will be almost white, maybe an almond color, the black mix band will be a charcoal color. The longer the run, the darker the color.
The overall insulator color on a used plug reflects it's compatability with the engine temperature. The plug should be a light tan to chocolate brown with out any spoogey, black stuff on it. It should always be fairly clean and dry. If the plug is too dark, it is an indication that it's temperature range is not compatable with the engine operating temperatures. Now if it is dark and wet, then the motor is just running too rich and you really can't tell if the plug is the right heat range or not.
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Post by canyncarvr »

Another note on plug reads:

Anyone checked CDave's recent (well, since I last looked at it) write up? As I understand it, he isn't correct. He says the darker the band, the richer the burn.

I understand it to be as Ski said..the darker the band, the LONGER the burn was, but it's the thickness of the band that you are interested in when checking mixture.

I missed something earlier...CEK vs: DEK clip positions:

Yes. #4 on both. No...they aren't at all the same in 'personality'...but the clip positions were the same on both. The DEK has a longer straight section (not longer L1...longer STRAIGHT) that makes it act considerably different.

A 155 main on a 220 would seem pretty rich to me. A 155 in my bike will make it fall flat on it's face performance/topend wise. Takes a hit on the bottom, too. Yes...what I run/what you run can't be at all compared, but 220's (modified or not) generally run a leaner jet set than a 200. At least, that's been true when comparing others and their 220 setups.

Whatever works.

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