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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

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.

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.

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?

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.

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.

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 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.

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.

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.

I had a fairly lean setting, (sea level to 3000 feet) using a 152/40 setup with AS about 1 turn out. Still had a lot of spooge using Maxima Super M. Started reading about flash points and then switched to Motul. POOF-no more spooge! Maybe a small trickle after hours of slow rock crawling and trails. So Im not sure if its all about lean jetting....Ive been at 40:1 since I got my KDX's.

TwistedRoot wrote: ↑12:21 pm Oct 04 2022 So Im not sure if its all about lean jetting...

I tend to agree. It is just one of four factors. The jetting, the flashpoint of the oil, condition of your top end, and how you ride all affect spooge.