RB Designs: How sensitive to temp change?

BRush

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Since installing my RB Designs carb, the settings that have worked well are: 155 main, 42 pilot, needle (AEG) on the fourth clip. Air screw 1.5 turns out. Up till now, riding temps have been between 65-72 deg F. The off-idle response has been really crisp. This last weekend, though, the temps got up into the mid-80's and suddenly I'm seeing the rich "gurgle" from just off idle to about 1/3 throttle starting to re-appear. Opening up the air-screw did not seem to help much (but I only made minor changes). I did not really get into it because there's a time for jetting, and a time to just shut-up-and-ride :)

My question for you fellow KDX'ers with this mod: Do you find the jetting with the RB Designs modified carb any more, or any less sensitive to temperature changes than an unmodified carb? My seat-of-the-pants opinion was that the stocker is maybe a bit less sensitive. I should also say that I still need to look at the plug and check the reed condition to see that nothing's changed - but it feels like a jetting issue. Also, based on where the 'gurgle' appears I'm trying to decide if it is a needle issue or a pilot jet issue. Any opinions?

Thanks.

Motor: 225cc big bore kit, w/light porting.
Air-box mods
FMF torque pipe
power core silencer
plug: BR7ES
Boyesen power reeds (#607)
Fuel: pump gas (Mobil unleaded premium)
Altitude: 1000ft
 

WoodsRider

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#2
You said it!
Originally posted by BRush
... just shut-up-and-ride :)
j/k BRush, you might try dropping the pilot down to a 40 especially now that the temps and humidity are rising. When you say fourth clip on the needle, are you referring to the fourth groove from the top, as it sits in the carburetor?
 

BRush

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Re: Re: RB Designs: How sensitive to temp change?

Originally posted by WoodsRider
When you say fourth clip on the needle, are you referring to the fourth groove from the top, as it sits in the carburetor?
That's the one.
 

WoodsRider

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Change the pilot, that should clear up the off-idle "gurgle" you're experiencing. This weekend should be great for testing it out. If you find it still a tad rich between off-idle and wfo, raise the clip one groove. At catraland you'll spend a lot more time on the pilot and needle than on the main. ;)
 
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#5
Just so you won't feel lonely..

re:
Do you find the jetting with the RB Designs modified carb any more, or any less sensitive to temperature changes than an unmodified carb?
Yep. And about everything else, too! Because it's more likely to change faster where I currently ride, I've found elevation to be a big factor, too. I can feel the difference on the way UP!

Temps, too. In the spring with the temps dropping quickly as soon as the sun went down, my bikes personality would change right quick!

Hhhmm..about that dial-a-jet.........? Makes me wonder. Let's see...that was thundersproducts.com?? ;)


BTW...why doesn't Keihin make the bowl/bowl plug just a teeny bit different so you can change the pilot by taking the plug out? You can SEE it..but can't quite get
 
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BRush

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#6
Originally posted by canyncarvr
BTW...why doesn't Keihin make the bowl/bowl plug just a teeny bit different so you can change the pilot by taking the plug out? You can SEE it..but can't quite get
Yes it's pain that the pilot takes a minor production to change. I wonder if you could take one of those oversized Boyesen float bowels and engineer in a second access port? On the jetting front, Instead of dropping the pilot to 40, I dropped the main from 155 to 152 (something I've been meaning to do anyway) and tried to use the air screw to compensate for the pilot. The temps worked their way up to 83-84 degrees with massive humidity (which also reduces air density). 1.5 out was too rich. Backing out in 1/4 turn increments to 2 turn out cleared things up a good bit. That's where I rode most of the day, but I could feel that it was right on the edge of "too rich" . If I have to go too much more, I'm going to drop the pilot again.

Every time I read a post now about someone discussing their RB Designs jetting, I note the settings down in a file. I have seven or eight entries and it's a good reference for seeing where I stand. I think I have you down for:

  • Main 152
  • Pilot 42
  • Needle AEN
  • Clip # 4th
  • Air Screw 0.5
  • Slide Cut #7
  • Bike 200
  • Ported? No
  • Elevation ?
  • Temp ?

Do you still run that setup?
 
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#7
If I recall correctly, the Boyesen bowl is a pretty roundy thing. Would be hard to put in an access with no boss to put it into.

Gee..you keep good track! Your setup is so different from average..big bore, ported and all..you may well be in your own speshul place as far as jetting goes.

I put in a rad valve two weeks back. I dropped from a 150 main (which had WOT checked OK) to a 148 based on the 'drop a size or two' notes from Boyesen. Not a good idea. For one thing, I went on reserve @ 50 miles. THAT was a surprise. Later did a WOT with the 148. Oops! Plug was clean as a pin. Spotless. No color at all. Wasn't a brand new plug, but fairly. I'd just fouled one probably 45 minutes earlier (a B7ES).

What a strange juxtaposition of circumstances!

Rode the next weekend: 42-150-AEN/3-AS/.5. Didn't foul a plug during the ride. Didn't get to a decent WOT check spot, either. I went out 5/8 on the AS. Response took a dive. @ .5 it was perfect.

The 5/8 out setting made the bike a tad slow on the uptake in 2nd gear..and when it hit it hit hard! Too hard to be able to control it well on a granite, slippery, rooty, rocky uphill. Too much of an inadvertent wheelie opportunity (read, 'he looped it!'). With just 1/8 in..completely different story. Lost the 'slow on the uptake' part. Traded the 'hit' part for an electric motor-like strong pull in 1st and 2nd. Incredible response. It was great!!

Which is a long and boring way of saying I don't see how going to a 40 is going to work for me. I'll change plugs every weekend to keep that consistent, hard, even pull on uphills that I can barely even STAND on!!

We rode in a few spots last weekend where wheelspin was a bad thing. You wouldn't make it! And the uphills were long enough that there wasn't a 'head start' sort of chance.

Anyway..currently @ 42-150-AEN/3-AS.5

Temps: 75-85ยบ
El: 2000-3500' (from GPS)
Slide: Still the #7. I have a #6. The 'shutup and ride' applies to
that. Haven't taken the time to know more than it would take some
work to get that setup right.
FMF KG-35
PC S/A
Boyesen rad valve (carbon pro reeds..all they have for a kdx)

I know the RB mod makes the pilot circuit act funny. I'll try the 40 just to see if I can clean up the plug and still keep the strong pull I have now.

Oh..this is going to be important. I retarded the timing one 'notch'. The wonderful bottom end my bike has now is certainly due in part to that. Don't know how much, as I haven't changed the timing back to 'stock' (middle mark) except at my house. That's about 1300' el..and I know from past experience that I cannot jet the bike at the house and have it run for diddle just a couple thousand feet up! At the house though, I changed the timing back and forth a few times (all the fun of rejetting without the gas!) and really liked the retarded setting. I think that (timing) would be less of a 'environmental' (el, temp, humidity) issue, so I would expect the improvement to be better 'up' as well as 'down' at home.

Head to head with a similarly setup 200 (my riding buddy has a DeltaForce block that they made specially for him to check out), he couldn't catch me if I got ANY jump on him..I couldn't catch him likewise. Pretty close. His timing is 'stock'. My bike pulls MUCH better (sez me) in the off-idle area. He's probably 20# lighter than I am. That's gotta figure in there somewheres.

This KDX has really gotten under my skin. I swear I live for the weekend! I haven't had my honda out but once this year! I bought a vehicle and a trailer JUST to haul it around. Talk about a 'black hole'....oh YEAH!!