Need help with Race Fuel!

Hey guys. I have a 2001 Honda CR125 that I want to start running on race fuel. Can you guys tell me all the things that I will have to do to the bike to be able to run race fuel in the bike? And if I should run half race Fuel and half normal fuel? And things like what's the best brand of race fuel to use and what the cost of it is and if it is actually worth it in the long run! Thanks guys any info is appreciated!!

In a 2 stroke i think VP MRX02 would be a good choice. As for what to do to your bike, some jetting changes might be necessary. But remember that race fuel doesnt give all that much power, especially a 2 stroke. When you build a high compression performance engine, the race fuel will tolerate the higher compression without pinging or detonating. The mods make the power, the fuel allow to run the engine in that state of tune ''safely''. So if you have a stock engine, a 50/50 mix of pump gas/MRX sould be enough. Throttle response should be better, bike will run crisper but with only race fuel in a stock bike, you got to have realistic expectations.

 

here's a good guide from Motocross Action http://motocrossactionmag.com/Main/News/RACERS-GUIDE-TO-THE-HIERARCHY-OF-MOTOCROSS-RACING-10439.aspx

Edited by grogarage

Hey guys. I have a 2001 Honda CR125 that I want to start running on race fuel. Can you guys tell me all the things that I will have to do to the bike to be able to run race fuel in the bike? And if I should run half race Fuel and half normal fuel? And things like what's the best brand of race fuel to use and what the cost of it is and if it is actually worth it in the long run! Thanks guys any info is appreciated!!

why? It's stupid and pointless. Run 93. Pump gas and you'll be fine. Idk why people wanna run race fuel. It will cost you more money and will eat up pistons.

why? It's stupid and pointless. Run 93. Pump gas and you'll be fine. Idk why people wanna run race fuel. It will cost you more money and will eat up pistons.

because the highest octane I can get here is 89 and its horrible.

i run basic 87 unleaded in my 2009 yz250. bikes never missed a beat. its a 2 stroke, you could fill it with poop and it will run the same.

Mix 32:1 and fill the gas tank. Ive ran 110 in my 01 cr125 with no problems. Throttle response is a lot better, but it works best mixed 50/50 with 93 octane. I only use it if I happen to be going by that gas station that sells it.

When you run race gas, 50/50 or all race gas. Do you have to change your jetting? Cuz I want to run race gas only at the races. Not all the time.

Yes the jetting will be different. Oxygenated fuel like mrx01 will need to be jetted much richer. I am running c12 and it seems to need to be jetted leaner

Yes the jetting will be different. Oxygenated fuel like mrx01 will need to be jetted much richer. I am running c12 and it seems to need to be jetted leaner

is there any way that I could mix my fuel at a different ratio so that I don't have to change my jetting or just by adjusting my air screw?

Yeah I have a YZ250 and am considering buying higher octane for two reasons. One the manual says to use 96 or up and I only have 93 around here. Two is the bike doesn't sound right when idling I believe its pinging but runs fine otherwise. I would have to drive a ways for it and would probably mix 50/50 or a 75/25.

is there any way that I could mix my fuel at a different ratio so that I don't have to change my jetting or just by adjusting my air screw?

nope

What would the bike act like if I didn't change the jetting and started to run race gas? Say, VP C9??

I run a cool season jetting and a warm temps jetting (usually by may) and in the hottest month of summer i'll run U 4.4 to avoid another jetting change. Other than that i just run AvGas all year to avoid the ethanol

To the guy who said it will burn up pistons you should not be giving others advise. Race gas actually runs cooler than pump gas. In a stock bike your not going to gain much if any power. You will experience slightly better throttle response and more consistant jetting which can be a plus. As for price I know vp110 at the local station was a little over 8 bucks a gallon last year. Which is cheap. Vp c12 is like 75-90 dollars for a 5 gallon can. You do the math. Your best bet is to go to your local small airport and get 100 octane low lead or 100ll. It will have a higher octane point than mixing 89 and 110/112 and is much cheaper. Plus no ethanol. To the guy that has the Yamaha 250 and his manual says to run 96. That measurement might be in RON which is different than your standard octane rating that we are used to in the states. I don't know the conversion but 96 RON is somewhere around 89-90 octane I would guess. Do your research before you just decide to switch. I think for what the original poster wants to do the 100ll av gas is the best option. Cheap, stable, and no ethanol. Dont run race gas on the weekends just for your friends to comment on how good it smells.

If pump gas is bad in your area, 100LL avgas is the best low cost option for someone that has a stock compression 2-stroke.

To the guy who said it will burn up pistons you should not be giving others advise. Race gas actually runs cooler than pump gas. In a stock bike your not going to gain much if any power. You will experience slightly better throttle response and more consistant jetting which can be a plus. As for price I know vp110 at the local station was a little over 8 bucks a gallon last year. Which is cheap. Vp c12 is like 75-90 dollars for a 5 gallon can. You do the math. Your best bet is to go to your local small airport and get 100 octane low lead or 100ll. It will have a higher octane point than mixing 89 and 110/112 and is much cheaper. Plus no ethanol. To the guy that has the Yamaha 250 and his manual says to run 96. That measurement might be in RON which is different than your standard octane rating that we are used to in the states. I don't know the conversion but 96 RON is somewhere around 89-90 octane I would guess. Do your research before you just decide to switch. I think for what the original poster wants to do the 100ll av gas is the best option. Cheap, stable, and no ethanol. Dont run race gas on the weekends just for your friends to comment on how good it smells.

thank you! Some good answers in there that I'm looking for! But one more thing like I posted before. Did I absolutely need to change my jetting if I run on the stuff your telling me that I should? Because I really don't wanna change my jetting because for me right now it is perfect so that way I can run race gas at races and durning practice and not for just putting around.

Yes you will have to rejet. T the mrx02 fuel required so much richer jetting that without changing jets it would run extremely lean to the point of engine damage.

And if you left it jetted for race gas while using pump it will run so rich there wi be spooge everywhere and will not run well.

its an 01 stock cr... is it worth it. save that money for tires and chains.

for what you have and what youre trying to do theres little benefit using race gas. If you got your head milled to bump up the compression a bit, you could run AvGas ....id just run 93 and keep it the way it is. You need hi compression to get the major benefits of race gas, not stock...save your munny

I'm really trying to be patient and not be mean, but I honestly would bet 1,000 dollars cash right now that your jetting is not perfect. Just trust me and everyone else here and don't run race gas on the weekends. I know its cool to say I run race fuel and I'm racing the bike so I need race fuel and whatever, but there is no reason for you to do so. Since I am positive that you don't know how to properly jet a carburetor (not dissing you) don't mess with a different type of fuel or oil mix ratios. If anything get the 100ll av gas from your local airport and have someone that knows what they are doing jet your bike for you. If no one in your family or your friends family knows there way around a dirtbike really well then there is a section on this site where you can talk to people local to you. I am willing to bet if you go to your local discussion board on here and ask for help that someone will be willing to do that. Being young is tough because all your buddies talk about the engines and doing this and doing that and then a few years down the road as you learn more you realize those people that you thought knew what they were talking about really didnt know jack shit. I don't want to be the one replying to your posts trying to talk you through an engine rebuild if you blow up your bike because you ran race fuel and didnt rejet your bike.

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