Race Gas or Super

Rich, I just jumped on to this topic to see what everyone had to say about race fuel for their YZ400/YZ426 bikes. We have a YZ250F that we race moto-x with in the 125 intermediate class (my son does the racing). You mentioned that a racer would feel increased throttle response (probably the same kind of difference we felt when putting race gas vs. pump in our 00'YZ125), and a power difference over 6000RPM. My son is on the rev limiter most of the time. I've wanted to use race gas, but have 7 questions. #1 Does race gas hurt the motor like Motocross Action Magazine says? #2 Does jetting changes associated with race gas only require only a main jet change? #3 I think either Sunoco or VP have a leaded race gas. Would that be better from a reliability standpoint? #4 Would mixing 50% race gas/50% pump be worth the benefit? #5 Will race gas produce less carbon build up on the valves? #6 I live close to a VP distributor which VP gas would you suggest? #7 Do you believe that race gas shortens the life expectancy of the motor? Thanks in advance for your answers.


since i race a 01yz250f i can help you on your questions. plus, rich and i have talked quite abit about this already in private and on DRN in public.

1) Motocross Action is full of bunk. no truth what so ever in their statement.

2) as always, jetting requirements are associated with your atmospheric conditions at that given time. jetting changes will be much more radiacal if you run an oxygen enhanced fuel like MR2. however, i can tell you that for me, running VP C12, i have so far only changed the main jet up to a 180 (for the cold) and will probably drop it down to a 178 or 175 when we see the 90's in a month or so.

3) lead in the fuel certainly is not a bad thing. helps lube the valves some. heck, old hot rods used to require it (muscle car era).

4) don't mix. just a waste of money unless you are trying to control a pre-ignition or detonation problem. run it straight for best results.

5) i can't comment on carbon build up, sorry.

6) all of the vp fuels are better than pump swill. if you can afford it and want the ultimate performace, go with MR2, but you will have to rejet the entire carb. next best is probably gonna be C21, then C19, C18, C12 and the cheapest (yet better than pump) VP Red. at this point, i'd suggest C12 and learn what it does for your bike.

7) shorter? if anything it would extend it by burning cleaner and not leaving as many deposits to contaminate the oil. however, you should be changing your oil frequently on a race bike.

Originally posted by Clod Thrower:

What about octane boosters I can get at the auto parts store? Some will treat 20gal & they are cheap. Will they hurt my 426?

I take it these won't help me. How about it guys???? Some have a lead substitute in them.

Ok, So how does AVGAS compare to pump gas and race gas?

I know it is different for a lot of reasons but a friend of mine runs 100ll in his 00 426 and it runs great. I have only used pump gas so far but have been thinking about trying a tank or two of AVGAS.

I know airplanes run at 3000 rpm, 12,000+ feet and sub zero temps.

I also know that I ran it in a chev 350 stock car at 12:1 comp and it worked pretty darn well.

What do you think?

Rich & SUnruh,

Have you heard of a VP fuel called MS103 ?

I talked to World Headquarters for VP and there Tech said this is the fuel that the White Brothers used while testing engine performance on the 426, and said it produced the best power gains they had seen.

I run at sea level very high humidity 100 deg temps, and have a carbon build up problem I am trying to eliminate the carbon build up by using race fuel, I am allready jetted leaner than stock and the pump gas builds carbon bad in the exhaust port area.

If you have any info it is ceartainly appreciated.



Beaumont, Tx.

01 426 #67

Octane boosters for the 426 is not what we are looking for. The most important criteria when considering a fuel for this application would be the RPM range. Since this machine redlines at 11,200, selecting a fuel that will burn optimally approaching this redline is the goal. Octane boosters merely help to prevent detonation before the ignition and the damage that constant pre-ignition detonation(knock or ping) brings with it.

From my own research, a good choice of the proper race fuel covers all bases...plus...the quality of the proper race fuel makes jetting quite a bit easier and much more accurate and consistent.

Personally, I use VP C-12 for a couple of reasons. First, it's available and packaged correctly. Next, I have my 426 jetted perfectly for this fuel. It's also priced so that I haven't had a coronary yet. I can't justify spending twice and maybe even three times for a fuel that would increase my bike's power output. I'm 47 and ride too cautious to take advantage of that. I've found my comfort zone... :)

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