premix ratio ?

[midlifemoto]

Hi, just getting into vintage racing and have a couple of projects just about ready to roll, 79 CR 125 and 78 RM 250....the manuals say to mix at 20:1. I run 40:1 in my new KDX though the manual calls for 32:1. figure that's not leaning it out too much.

Trouble is, I don't want to carry around different cans with different mixes, 40:1 for everything would simplify things.

However, from the factory recommendation of 20:1 to 40:1 is TWICE as lean. Is that acceptable? I was thinking maybe just run everything at 32:1 as a compromise but my KDX is jetted perfect at 40:1.

Thoughts? Thanks!

 

[BigRedAF]

32:1 is fine, you may depending on your bikes current tune need to re-jet.

From the info you posted this is probably going to shock you...

40:1 is richer than 20:1 not leaner. Richness is in reference to AFR, (air/fuel ratio). If that's hard to grasp try to understand it this way. Fill two 8 ounce jars with your two pre mixed batches of fuel. One at 20:1 and one at 40:1. Both jars have 8 ounces of fuel and oil. Which one has more gas in it? The 40:1 has more fuel and flows faster therefor it's richer and will need to be jetted leaner if your bike was running perfect at 20:1.

I had a 78 RM125C, it did call for 20:1 but that was over kill. I ran that bike with Yamalube-R at 32:1 and it did well.

 

[midlifemoto]

thanks....i run Yamaha 2 R in everything 2 stroke, my bikes, outboards....I'm a believer in it....sounds like 32:1 is the perfect compromise for all my dirt bikes new and old

 

[2strokerfun]

thanks....i run Yamaha 2 R in everything 2 stroke, my bikes, outboards....I'm a believer in it....sounds like 32:1 is the perfect compromise for all my dirt bikes new and old

As a general rule of thumb, a lot of people believe you can't go wrong with 32:1

 

[tony91]

As a general rule of thumb, a lot of people believe you can't go wrong with 32:1

+1

 

[jtlracer0707]

i have a 01 Xtremmachine tantrum 50cc i was looking for some help on fule mixture,i dont like the oil tank runs to rich and bogs out,what do u think

 

[jtlracer0707]

+1

32-1 is good for 50cc quad

 

[tony91]

Sounds like a jetting issue.

 

[jtlracer0707]

what does that mean

 

[tony91]

You need to tune the carburetor. These will get you started:

http://justkdx.dirtrider.net/carbtuning.html

http://www.cyclewerksracing.com/Carb%20Tuuning.htm

 

[sixds]

if your quads injection system is anything like a snowmobiles, it will have a way to adjust how much oil gets goes into the carb.