What premix ratio should I use with the RB carb

Questions and Answers about the best carb and Head mods available for the KDX.
Post Reply
JZ05220r
Member
Posts: 104
Joined: 12:36 pm Mar 28 2021
Country: United States

What premix ratio should I use with the RB carb

Post by JZ05220r »

I noticed RB sets the carb up with seemingly lean jetting, for example mine will be 40 pilot 150 main. Was their ever a recommendation from Ron on what premix ratio he intended us use with that jetting? (Purchased second hand) I’m currently running 52:1 per Jeff Fredette’s recommendation. (220)Thanks
User avatar
doakley
Gold Member
Gold Member
Posts: 1220
Joined: 02:58 pm Mar 10 2016
Country:

Re: What premix ratio should I use with the RB carb

Post by doakley »

It shouldn’t matter. FWIW I run mine with RB carb at 50:1.
Also, I had to lean mine further after receiving it. Every bike is slightly different.
User avatar
SS109
KDXRider.net
KDXRider.net
Posts: 5180
Joined: 05:11 am Aug 23 2009
Country: USA
Location: Tucson, AZ, USA
Contact:

Re: What premix ratio should I use with the RB carb

Post by SS109 »

doakley wrote: 01:54 pm Sep 04 2022 It shouldn’t matter. FWIW I run mine with RB carb at 50:1.
Also, I had to lean mine further after receiving it. Every bike is slightly different.
Exactly! Pic a mix and stick with it. I run 40:1 myself. I also had to lean out the main jet more from RB's included jetting.
AZ State Parks OHV Ambassador - Trail Riders of Southern AZ
'11 GasGas EC250R
Current KDX: '98 KDX220
Old KDX: '90 KDX200 -White/Blue
My Youtube Channel: WildAzzRacing
JZ05220r
Member
Posts: 104
Joined: 12:36 pm Mar 28 2021
Country: United States

Re: What premix ratio should I use with the RB carb

Post by JZ05220r »

doakley wrote: 01:54 pm Sep 04 2022 It shouldn’t matter. FWIW I run mine with RB carb at 50:1.
Also, I had to lean mine further after receiving it. Every bike is slightly different.
Ok, thank you. What did you end up settling on for your jetting, just curious?
JZ05220r
Member
Posts: 104
Joined: 12:36 pm Mar 28 2021
Country: United States

Re: What premix ratio should I use with the RB carb

Post by JZ05220r »

SS109 wrote: 03:52 pm Sep 04 2022
doakley wrote: 01:54 pm Sep 04 2022 It shouldn’t matter. FWIW I run mine with RB carb at 50:1.
Also, I had to lean mine further after receiving it. Every bike is slightly different.
Exactly! Pic a mix and stick with it. I run 40:1 myself. I also had to lean out the main jet more from RB's included jetting.
Ok I’ll probably end up going with 40:1 I ride some tight woods but also ride a lot of higher speed terrain and could use the extra oil for those high speed situations.
User avatar
doakley
Gold Member
Gold Member
Posts: 1220
Joined: 02:58 pm Mar 10 2016
Country:

Re: What premix ratio should I use with the RB carb

Post by doakley »

JZ05220r wrote: 07:03 pm Sep 04 2022
doakley wrote: 01:54 pm Sep 04 2022 It shouldn’t matter. FWIW I run mine with RB carb at 50:1.
Also, I had to lean mine further after receiving it. Every bike is slightly different.
Ok, thank you. What did you end up settling on for your jetting, just curious?
H HA! Honestly, I don't remember. I'll look next time I'm at the shop. It was the pilot jet I changed, not the main. Again, every bike is different. I would suggest you go through the entire jetting procedure with a new plug.
User avatar
Molly's 70
Platinum Member
Platinum Member
Posts: 480
Joined: 04:29 pm Jun 18 2017
Country: USA
Location: Wichita, Kansas USA

Re: What premix ratio should I use with the RB carb

Post by Molly's 70 »

My understanding is 50:1 (I use Amsoil) is faster lubrication because the fuel mix is lighter in weight. Faster lubrication is better than more oil put into the premix.
If you lend someone $20, and never see that person again, it was probably worth it.
John_S
Gold Member
Gold Member
Posts: 746
Joined: 06:59 am Jan 27 2017
Country: US
Location: Florida

Re: What premix ratio should I use with the RB carb

Post by John_S »

If I understand correctly it’s not faster lubrication but it is a thinner mix when you use less oil.
Less oil means richer fuel mixture and more oil is a leaner fuel mixture. Only talking about the amount of combustible fluid per given amount of premix.
If a bike ran perfect at 40:1 and you put in a tank of 60:1 your bike would run rich. 20:1 and it would run lean until you change the jets to match the “viscosity” of your premix.
That’s why a lot of guys on here say pick a ratio and stick with it.
Less oil equals smaller jets.
More oil equals larger jets.
User avatar
KDXGarage
KDXRider.net
KDXRider.net
Posts: 13665
Joined: 06:45 am Nov 01 2004
Country: United States of America
Location: AL, USA
Contact:

Re: What premix ratio should I use with the RB carb

Post by KDXGarage »

Anyone ever see a small pool of oil in the bottom of the crankcase when changing a piston? :-) That oil is what gets flung around by the outer circumference of the crankshaft to lubricate the parts. At 6,000 RPM's, that is 100 time per second. That is some fast lubrication! :-)

On a serious note, if you have a larger pool, that is cool for drag racing up sand hills in the summer time, but horrible for following the grandkids around in the backyard. Each of us is usually somewhere in the middle of those two extremes. Jet for your bike and situation.
Thank you for participating on kdxrider.net. :bravo:
To post pictures from a device: viewtopic.php?f=88&t=24128
JZ05220r
Member
Posts: 104
Joined: 12:36 pm Mar 28 2021
Country: United States

Re: What premix ratio should I use with the RB carb

Post by JZ05220r »

KDXGarage wrote: 06:50 pm Sep 06 2022 Anyone ever see a small pool of oil in the bottom of the crankcase when changing a piston? :-) That oil is what gets flung around by the outer circumference of the crankshaft to lubricate the parts. At 6,000 RPM's, that is 100 time per second. That is some fast lubrication! :-)

On a serious note, if you have a larger pool, that is cool for drag racing up sand hills in the summer time, but horrible for following the grandkids around in the backyard. Each of us is usually somewhere in the middle of those two extremes. Jet for your bike and situation.
I plan on riding it hard so I’ll stick with 40:1 for now.
Post Reply