C12 in a 250r...ya or na?

I have some leftover c12 from my 2 smoker...Ive heard people saying it was ok to run in thumpers and others saying it was a big no, So what are your opinions?

Id probally wanna run It straight, and just for races, Ill stick to 94 for practice.

What jetting changes will I have to make, will it run leaner or richer on c12? Id Liek to get it jetted so it runs decent on both..but thats pushing it.

From the VP website:


The best all around racing fuel made. Recommended for CRs below 15:1, satisfying the needs of 75% of today's race engines. One of the winningest fuels in racing history, including Modified Tour, GNN, D.I.R.T., Indy Lights, NHRA, AMA as well as other local and national championships across the U.S. and around the world.

• Color: Green

• Motor Octane: 108

• Specific gravity: .717 at 60° F

Really only benificial if engine is modified...ie high comp piston etc IMO.U4 will give more power.

The lowest octane rating you can run without detonation, the more power the motor will make. Your motor was designed to run on pump gas. 108 motor octane is not needed. Running C-12 straight, the bike will lose just a tad of its crispness. Running a 50/50 C12-93 unleaded mix will best serve you and the main benefit will be the lead in the C12 will help valve wear a little. Just my 2 cents. :) Oh and jetting is not affected.

1. Is your bike jetted properly on pump gas ?

2. If so then C12 will be slightly richer, Air Screw maybe 1/4-1/2 turn in, I clip up on needle and I main jet smaller. You have to test.

3. If your bike has stock jetting that is a tad lean by most standards with pump gas then C12 will be fine.

4. If you run race gas stay with it do not switch back and forth IMO. At the least run C12 for races then do a 50/50 with 93/94 pump for practice.

5. You do not need Hi comp or a cam change to run C12 it will work well in a stock motor. The Octane will NOT kill power like some say. Generally C12 and others burn completely and give a better seat of the pants feel when set up (throttle response).

6. Fuels like U4,U2 or MS109 from VP work very well due to there extra O2 and specific fuel curves. They are pricey and maybe not really worth it for everyone.

The lowest octane rating you can run without detonation, the more power the motor will make. Your motor was designed to run on pump gas. 108 motor octane is not needed. Running C-12 straight, the bike will lose just a tad of its crispness. Running a 50/50 C12-93 unleaded mix will best serve you and the main benefit will be the lead in the C12 will help valve wear a little. Just my 2 cents. :) Oh and jetting is not affected.

I would like to hear why so many people say that the Octane kills power. Maybe in the old days with race fuel or generic fuels like CAM2 but now there is so much custom blending for an application. The benefits of the proper fuel curve and added components of a specific motorcycle race fuel will out weigh any negative effect (very very small) of the octane components added to the fuel.

The 04 CRF will respond better to a fast curve race fuel better than the 05. The 05 intakes ports should mix up the fuel and air better than the sewer pipes on the 04...just my theory.

this sounds noobish but, what kinds of power/changes in the motor will a high comp piston give you?

Ok, mied thoughts...One question...Will it in any way hurt my motor? Will it reduce its life expectancy at all? And can it hurt the coating on the TI valves? Im not really looking to go and buy c12 all the time, I just have about 5-10 gallons left I need to finish off. If it wont hurt my motor ill try some out...

i ran it in my smoker and loved it....so maybe itll be like that?

I ran it in my 80 all last season, I didnt change the piston except for at the beingining of the season, Its also been the same crank for two years (one year on pump, one year on c12) My cranks have usually only lasted a season. And I normally needed a new piston and rings mid season, I tore into the bike mid seasona dn the stuff looked so good I didnt change the piston, I think the better gas, and a bike jetted right will perform better and last allot longer. But I dont really have the money to feed my thumper race gas all season, Its plenty poerfull, I had to squeeze all the power I could outa my 80 because I was quite big on it....ANd it wasnt verry powerfull to begin with, Plus I needed to run it because the motor work it had done at RPMs

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