Data Poll - RB Carb Mod for 200's

[Fred T]

A little plug for the RB carb. Last season we went for a ride in early December -last ride of the season before winter rebuild and RB mod. Yesterday I rode that same area and there is a pretty good size hill in one of the sections. Last year it got up it pretty good but ended up screaming in a lower gear at the top. Yesterday I went of the hill flying in a taller gear and had wheelie power at the top. The hill has large corners in it and some large berms that if you ride the upper lip of the berms you can carry lots of momentum on them and I was flying around the corners...major fun and major improvment in power from the motor. I was shocked at how much HP it was making up that hill. Second scenario was a guy on a modded KTM 200 MXC hooked up with us for a ride. The laundry list of mods he did to his bike included some porting, pipe, reeds and some super dooper engine oils. Well when we got out to a road he taunted me into a little drag race so I dropped the hammer on my little KDX and power shifted through the gears expecting this mighty KTM to inch on past me...but it never did. Again the RB carb is making more HP with that magic CEK needle. If you don't have this mod on a 220, get it!
<end of rant>

 

[70 marlin]

sounds great! where'd this all happen? leota?

 

[Fred T]

Yep!

Originally posted by 70 marlin
sounds great! where'd this all happen? leota?

Yesterday at 50 degrees I was 40 pilot, CEK#4, 152 main. 1200 feet ASL, 93 pump gas-MX2T 40:1.

 

[fred2]

Fred T,

I have a 97 220 am presently getting a carb and head mod from RB. Is it really that much of a difference? I hope it is. It sounds like the settings you just posted are the best ones, huh?

 

[canyncarvr]

fred2: re: '...the best ones.'

Be careful along these lines. The 'best ones' as far as jet-sets is going to be a highly individual matter. There's a LOT of input here (DRN) regarding jetting and specific information on the RB carb mod.

If you approach it from the standpoint of, 'This is IT!!,' you'll be dealing yourself a whole lotta short shrift.......which is to say, not getting the whole story.

FredT: How much was this the carb...how much the 'winter rebuild'? Did you do a topend on a tired bike???...or is most of your improvement the carb, 'ya think?

33-to-36mm DOES make a bit of a difference, huh?

Glad you like it!! ;)

 

[fred2]

CC,

Good point. I plan to review your archived posts on the settings you guys used and go from there to find what works for me.

Can't wait to get the mod done and dial it in!!!!

 

[jason]

Well I finally got to ride my bike yesterday! The only problem was that everybody I ride with was going to the GNCC. So that is where I got to ckeck out the carb. I did not get my 40 pilot so I had to run it the way I got it from RB. It seems a little sluggish picking up from idle till it comes on pipe. There were a few hills in the course that I was thinking I could lug up but it still needed a down shift to get up.

So I guess I do have a question for everyone. With the new pilot and maybe moving the needle down one clip, will that help the response? I still have not had the chance to ride in my usual slower single track trails and I am wanting to get some better response out of the carb. Right now it does not seem any better than stock.
Please help.

 

[Jim Crenca]

Remember back to last July when we were fighting with the AEN needle the carbs were shipped with? I was re-reading old notes from my log book and realized how much more consistant the bike runs now in regards to temperature, elevation, & humidity. I had the same jetting in at 400' and mid 60's temp in January, and then 32 degrees at 1200 feet in February, and, while the throttle response wasn't perfect, it wasn't horrible either. The new jetting is much more consistant in my memory (and notebook).

I too believe that the research by Dan, James Dean, Fishead, Fred, BRush, CC, etc. should only be a guide if you are looking for the sharpest jetting.
My 1994 (with pipe, silencer, air box mod, pump fuel, 400' elevation, and 70 degree temps) works best for me as follows:

CEJ needle in mid position
A/S usually at 3/4 turns
38 pilot; B8ES plug, and
165 MAIN JET - and I swear there are no air leaks or other problems; the thing wants a main jet that is way richer than the rest of you guys and runs great, and starts on the first kick. I think that we all agree that the main should be on the rich side of perfect in order to compensate for sudden changes in temp, elevation & unreliable pump fuel.

Anybody playing with race gas? I've got a fresh can of C-12 and am looking for suggested starting points.

 

[fishhead]

Jason,
It would be helpful if you could confirm what jet package you ran and the temps and altitude.

Jim,
one of my riding buddies has a 91 or 92 that likes a rich main as well at least a 160 or it pings like crazy. he is working with a cgk and cgj needle I would try your regular jetting with c-12 to start. you might find you can lean it out without pinging or overheating if the final endpoint of the evap curve is higher than your pump gas. I like c-12 because the initial evap point is low enough to give good throttle response and the end point is high enough to provide a little cooling and make jetting a bit easier. I agree with the findings on the a taper needle. It was way too lean on the taper so the power was falling off as you approached the 2nd half throttle opening. It was very noticable on long pulls up steep hills, I did a lot of testing on a section I called Dyno Hill because it was long enough and smooth and steep so I could put a good load on the motor and see how it liked the jetting. I found the b taper needles surged at 1/2 to 3/4 throttle so I tried the c taper and the results came in good.

 

[canyncarvr]

jason
Certainly check what's in your carb to start. Something to keep in mind, too is the touchiness of the AS. Adjust it by small (1/16) increments to find your sweet spot.

What you describe is !!exactly!! what I get with too much AS. Common knowledge doesn't put the pilot in a critical role in this situation (uphill pull of your bike in a higher gear with a good bit of throttle), but I can change my bike from flat to perfect with just a tweak of the AS. When it pulls well there is less of that 'hit' stuff, too, because the bike isn't recovering from a just-previous flat spot.

To reiterate...again ;)....as fishhead said, 'lowering the needle a clip' is shooting in the dark. You've GOT to know where you're starting from. Well..ok..he didn't say that at all...but I'm SURE that's what he meant!

At least the needle numbers aren't ground off like they used to be!!

 

[jason]

Fishhead,Canyncarvr, my jetting is cek 3,42,152 a/s 2 1/4.Air box removed,pro circuit p/s,power reeds,temp was 80-85,not sure of elevation (didn't bring GPS) was at Loratte Lynns in Tenn.
I have not messed with jetting very much,but I have been learning alot in the last couple of weeks by reading the thread in the archive and this one.
I was under the impression that if the a/s was turned out more than 2-2 1/2 turns that a size smaller pilot was needed.Is this correct?

 

[fishhead]

sluggish from idle to taper probably indicates you are lean on the A/S or straight section of the needle as CC said. You might try turning the A/s in to 1.5, A cej-3 needle, and cek-4. If it falls off the pipe on a long pull try a ddk-3 or a dck-3 to start.

an afternoon spent testing on a 3mile loop with some hills testing needles and clip positions will tell you a lot. Take good notes and record altitude and temps with the subjective notes of each combo. In no time at all you will be changing needles in about 3 mins.

 

[canyncarvr]

re: 'I have not messed with jetting very much'

That's going to change :)

The BEST thing you can do with your bike is jet it right. THAT means changing jetting from time to time, and getting to know when to do it, and what to do.

It's more complicated than figuring out how to pour pee out of boot whilst reading the directions on the heel..but it's not fixing apollo 13, either!

Did you check out the chart on CDave's site? The one that shows different throttle positions as related to carb circuit function? That's a valuable tool. You can mark your throttle by 1/4s to see exactly where in the range a problem is happening. Applying that info to the chart, you can get an idea of where to start.

Your AS @ 2.5 is likely INcorrect. I don't see this point on this thread...the AS is adjusted to BEST THROTTLE RESPONSE!!..not high idle. High idle is a place to START, but unlikely it will stay there. Turn the AS 'in' (CW) until you get no hesitation in 2nd gear with a quick flick of your wrist.

FredTs jet list is going to be real close..you aren't too far off right now.

One other thing to keep in mind...the carb chart shows a bunch of overlap. It's even more than the chart indicates. You can effect idle performance and off idle response with a way off jet needle setting, or a way off main.

The way to approach jet selection is to jet the main FIRST, and the only way that is reliably done is with a WOT plug chop with a consequential plug color check.***edit 11-5-04** It's not plug color as in tan, brown, chocolate or anything of the sort. It is the mixture ring at the base of the insulator..it's thickness that is where the A/F mix is found. Generally best seen with the threaded shell removed, you're looking for a band of pretty much no color..but pretty much gray or black that is around 1mm wide. Wider is richer, leaner (than 1mm) is looking for trouble.***edit 11-5-04**** That said, you're close with a 152. Maybe a bit rich..especially at 80-85º, not hugely so.

The correct way to jet is to go through the process yourself, using your own arse as a guide. That said, try 40-CEK/4-TV#7-AS@ 1.5, adjust for best throttle response from there.

Oh..if you're not used to jetting...make sure you correctly place the white nylon throttle cable retainer over the jet needle retainer nut. It's easy to miss getting the tab on the retainer into the corresponding slot. That'll screw up all sorts of 'response' issues.

See how any sort of written 'how to' that's going to cover every eventuality is going to be TOO involved? I promise you...keep after jetting until you get it sorted out and you'll be MILES ahead of a BUNCH of riders. You'll get to the point that your wrist and your butt will tell you exactly what's going on.

cheers!

***edit***

One more thing. Forget the idea of < 1.5 AS means larger pilot required. You may well end up just over 1/2 out. From that point, make changes no more than 1/16 turn at a time. It's pretty sensitive at that point. Something you may well change during the course of a ride, say if temps change > 15º or so (leaner-when-warmer).

 

[jason]

Thanks for the info CMy test ride planned for tomorrow got flooded out with the 3 inches of rain we got here today and dodging the tornados kept me from quality time from my bike!!
I plan on putting in the 40 pilot,then using the info from Justkdx to start from scratch (WOT plug chop,mark throttle,etc.).

Any thoughts on where a good starting point would be for some higher elevation riding? I am going to Colorado in 4 weeks for a 4 day ride and am needing to go ahead and order some jets. The starting elevation is around 8000ft and going to hopefully 11,000-12,000ft.That all depends on the snow line.Any help would be greatly appreciated.

But for right now I am more concerned with understanding and getting my bike right for home.
Thanks everyone for all the great info.

 

[Jim Crenca]

CC

Please give us more of that Jefferson Oregon speak:
"More complicated than figuring out how to pour pee from a boot..." was the only good laugh I had all day :)

 

[canyncarvr]

jason: CDave's site has a chart that shows jetting changes for altitude.

jim: One advantage of being old...remembering (maybe:( ) old jokes that youngsters haven't heard before...

And hey!! It's the STATE of jefferson!! We divorced ourselfs from that ******* or-ree-gone (otherwise known as the tri-met state, or 'greater suburban portland') years ago. Runs from roseburg to redding, ca...well maybe sack-a-tomatoes, ca, too!

..edit...huh??>> I got bleeped for libburral??? This is a politically correct site?? .....sheesh........

 

[jason]

I finally got to ride in my regular trails. I changed to the 40 pilot and dropped the needle one clip. It doesn't run like stock anymore!! It had a nice hit that could be controlled easily. Trails where slick in a lot of places but the wheel spin could be controlled with the throttle or if to bad just going up a gear. But when the trails where a little dryer there was no more having to clutch it out of the corners,just twist and hold on.

The only thing I noticed was that rolling slow in 2nd gear and going to WOT there was a slight hesitation. Is that a lean or rich condition? I tried turning the a/s in and it seamed to help some but I did not get to mess with it much(riding buddies getting bored watching me go up and down road).

40,CEK #4,152 a/s about 1 out (forgot to double check a/s before coming in) temps 68-72 alt 500ft

 

[fishhead]

Thats a lean condition, you might try a 42 pilot and a 45

 

[canyncarvr]

Yes. Lean.

But..the 'about...' part on the AS needs to be resolved.

Not to beat this real dead horse to death even summore (your 'about' comment begs more beating), BUT: adjust the AS for throttle response. I take your statement to mean throttle response isn't (responding that is)...so adjust it! Adjust by no more than 1/8 turns at a time. It takes less than that to have a huge impact on my kdx...but we wouldn't want to bore anybody!!;)

 

[Fred T]

Won't idle

I'm having problems getting my bike to idle when it's warm. It runs pretty good. I was thinking it might be a little rich on the pilot but I'm not sure as when it's was cooler it was lean so I figured that in 60 degrees it would be perfect. I tried turning the A/S in first and that didn't help and then I turned it back out - crisper throttle responce and pulls great on 1/4 throttle. Just won't idle when I come to a stop - I have to rap it to keep it running.
Setup:
RB carb, 220, stock porting CEK #4, 40/152- 93 pump gas at 40:1.
Yes, I took the carb apart bfore the ride to cure a little overflowing problem -gas was pouring out so i claned the carb out and tweaked one side of the float. I did not recheck flaot level though. Maybe that's it???
Thanks
FT

 

[Jim Crenca]

Fred,

Idle quality on my bike is much better at about 1 1/2 turns out although response is best at about 3/4 turns out. Last year when my floats needed adjustment (and float inlet valve needed replacement), gas would pour out of overflow tube yet engine idled fine. How does it idle with screw out farther?

 

[Fred T]

Jim
Thanks, I'll check. I think I am real close to 3/4 turns out on a/s now - it seems to idle slightly better than when I turned the a/s in...so maybe a 38 pilot is in the near future. As soon as the temps are consistently above 70 degrees I'll be making my "summer adjustments" to the jetting. I'm not much for jetting before every ride...I'm too busy so I bought JD's spreadsheet and plotted out jetting specs for varoius temps as the season changes. So far it's working pretty good.
FT

 

[Yobedoc]

Oops wrong thread!

 

[Fred T]

I'll be riding tomorrow so I'll check this idle thing but the weather is so screwed up I never sknow what to jet for. When it warms up the 38 pilot is going in.

 

[bbernardon]

Hi I am new to this forum and have read the jetting talk with great interest. I have a 98 200 bored to 220 and Fredette ported, K30, turbine core 2 arrestor, boyeson reeds. Going to a 152 from 155. 45 pilot for now; 2 questions: What is the RB carb mod and where would I find it; and my needle is labeled R1174K/2AFKQ, what does that mean? I ride mostly northern mich single track and any suggestions appreciated. Thanks

Bob