Race Fuel

my bike had the carbon stuff running down the pipe so i just changed from 40:1 to 50:1. i ran premium for both mixes.

....after that the carbon stuff never came back

here all the top mxers use race fuel. But they are too dumb to adjust the carb for it (jet it leaner) and often you can here momentary sputter/hesitation. You don't seem to of gotten anything but good results from it. What are the specs on that gas?

KD, how is the fuel you're buying sold? The specs on the leaded Trick look promising, if you could get it in sealed 5 gallon cans. After reading extensively on the value of race fuel, I tried to find either Phillips B35 or VP C-12 around St. Louis. Good luck - no one stocks either fuel, but I can have it special ordered and shipped for about $65 to $70 per 5 gallon can.

Consider yourself fortunate if you have a local retailer who stocks and sells enough volume to amortize the hazmat and shipping costs to a more reasonable level.

I also run VP C12 with Premium pump gas 1:1. Works well,but you do have to pay attention to jetting.

IMO, running race fuel in a reasonably stock (original compression & porting) only gives you consistancy from batch to batch that you won't get at the pump. I have found that crisp jetting is where the power really is, especialy response. I've experimented with C-12 and believe that my bike snaps a little better although overall max HP feels about the same. I have spent zillions of hours jetting for temp, altitude, humidity, & fuel brand and the main gain with C-12 is consistent response (assuming that it's fresh fuel stored in a sealed metal container, etc.

In the future, you may want to make one change at a time (like just a main jet or fuel change with same jetting) to realy know what caused what. I think that you made an overly rich bike closer to correct jetting and the fuel may have had very little to do with it. BTW, what did plug look like after WOT chop?

Search in Advanced Tech under "fuel" or "gas" and you will be amazed at the amount of info.

from lukesracing.com
"# Fuels- Some common misconceptions about race fuel are: 1. It burns hotter and can cause your motor to overheat 2. It will give your motor more power. 1. Race fuel is a high Octane fuel. Octane is a reference number that tells how much heat the fuel will withstand before detonating without a spark. Octane itself is a fuel similar to gasoline, it was given a rating of 100 to use a reference point to compare to gasoline. The amount of heat produced by a fuel is measured in B.T.U.'s. All gasoline's produce about the same amount of heat so race fuel will not cause your motor to overheat, in fact in most cases it will run cooler (race gas has additives that increase the cooling effect it has when it evaporates, like the cooling effect rubbing alcohol has on your skin). If high octane fuel was more likely to do engine damage they wouldn't use it in aircraft engines 2. Every engine requires a slightly different minimum octane to operate properly. If your motor requires 91 octane and your using 93 octane then it probably wont gain much from 108 or 114 octane race fuel. Most race fuels will require rejetting because the fuel carries more oxygen than pump gas, without rejetting it's possible that your engine will run leaner and produce less power. So why pay more for race gas? High octane race gas allows you to build an engine with higher compression, more spark advance or leaner fuel mixture, without detonating the fuel. The power advantages of race fuel come mostly from these changes. The higher oxygen content means you will run bigger carb jets to get the correct fuel mixture. Your engine will burn more fuel because it has more oxygen available to burn the fuel. Octane is just one of many specifications of race fuel. The specs of race fuel are measured and adjusted to the legal limits according to racing organizations. Every gallon is check and will be the same every time you buy fuel (if the fuel is fresh). Pump gas can vary greatly from one week to the next or from one station to another, and they only check samples of pump gas from thousands of gallons they produce. Different additives are added to pump gas according to the time of year and location where it will be used. In winter they add more alcohol to help remove moisture and they use additives to make the gas evaporate better at low temperatures ("vapor temperature"). Gas that will be used in very hot climates is given additives to lower "Vapor Pressure" to prevent "vapor lock". This is great for your car (especially fuel injected cars that measure and adjust fuel mixture electronically) but for a race bike it can alter your carb jetting from one tank of gas to another. The main thing to remember is to check carb jetting if you run race fuel, also remember if your going to go back to pump gas you may have to switch the jets back. In most cases stock 2 strokes run well on premium pump gas with the proper carb jetting and will gain little from race gas. Unless your building an all out "race only" motor I suggest using premium pump gas or mixing one gallon of race gas to 3 or 4 gallons of pump gas. Whichever you choose you should use it consistently."

that's all that counts.
if it works for you then go for it.
the article said that it causes the bike to run leaner and I've heard it said that KDXes come jetted too rich.

That's like saying you've added weight to the bike to slow it down because it has bad brakes. If the bike is jetted rich, re-jet it (IMO).

You've got a point there Jim but the article did also say that the race fuel had more of a cooling effect which would be advantageous over normal gas. But he should probably jet it leaner and then try it out with normal gas and then make the decision whether or not the race gas is worth the extra expense.

I know this may be heretical, but I really don't need any more power. What I WOULD like is all the throttle response & jetting consistency available. I would even trade a couple HP for instantaneous response that's linear to throttle opening, since I can use that everywhere. Most of the trails I ride I'm lucky to get 2nd gear wound out, and rarely 3rd.

 

 

If it works for you thats what matters. But if you don't have the compression that requires higher octane fuels then you are actually wasting tons of money and its losing hp. A KDX only needs 90 octane.

......... pump fuel here in Australia has been blamed for causing siezures during motoX races. It is pretty poor quality stuff (Some European manufacturers even have to re-jet their bikes at the factory before they ship them here just to run properly on our fuel).

"Aviation style" racing fuels have been banned in racing so riders have been forced to use fairly low grade pump fuel, even some premium pump fuels will not pass the regulations.

What american brands of fuel are available in Australia? Here there is Esso and Shell but I don't know that the brand names guarantee quality fuel.

Jag: Thanks for the credited info! I even read it...and yanno what? It's all right!! (there! THAT should make everyone feel better!)

The whole idea of more 'octane' being an absolute good thing is of course bogus. It can be just as easily a BAD thing as a GOOD thing. Actually, more likely the former than the latter.

re: vapor pressure

Every spring you can see STACKS of cars on the side of the road due to this exact thing. The 'winter gas' (modified to vaporize 'better') hasn't been changed yet and on a warm day the road that runs from the valley floor (1300') to the siskiyou pass (4000') at miles of 6% grade is littered with vehicles that just don't run on vapor lock! Imagine that!!

Anyway, thanks for the info!!! lukesracing has some good stuff!!

BTW...re: 'plug check........... a nice medium brown on the center electrode'

That (color) is an indication of plug temperature mostly, so doesn't directly say anything about A/F mixture (if that's what was meant). Air/fuel mixture is 'read' way down the insulator where it meets the plug shell.

Still, if the plug heat range is correct for the bike, plug temperature being effected by A/F mixture the color thing is not completely at odds with the conclusion.

...but it doesn't directly show A/F mixture. Not to mention which/how many of the 1/2 dozen carb circuits were being used at the time......

If it works don't fight it.
You might want to read the fuel article written by Rich that is also on Eric's site.
I think the reason that no one has explained why a low compression bike makes more horsepower on race gas is that there is no documentable reason based in physics that can support it.
Crisper response yes, but not more HP (IMO).

Engineers don't think that bees are aerodynamically able to fly.
Sometimes we just have to accept reality without an explanation for it.
If the race gas gives you more of a rush then by all means keep using it until you find a good reason not to.

You bet! And I run a couple º retarded because I like the result! Albeit a different result than what it's supposed to be, by 'rule'...but yanno what?

I really don't care! ;)