Racing Fuel??

6 replies to this topic
  • bigtom17

Posted August 06, 2002 - 07:37 PM


How does the stock Carb, react to racing fuel, I mixed it to premium 50/50 and it seems Like I had a extra hard time getting it started should this be??? Any users

  • qadsan

Posted August 07, 2002 - 05:35 AM


What kind of racing fuel did you use? Was it Aviation fuel 'Avgas' or what? What color was it, octane rating, brand name, etc?

  • mwespo

Posted August 07, 2002 - 06:34 AM


Unless you have a high compression piston installed you are throwing money in the trash. Just use the highest grade pump gas at the local gas station.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Portland_650R

Posted August 07, 2002 - 06:49 AM


Higher octane fuel burns more slowly, so, yes, it makes sense that it was harder to light. This is so the stuff will burn rather than explode at higher compression. Explosions, over time, crack pistons and do lots of other damage. I run 92 pump gas in my bike and it is fine - I don't hear any pinging.

One exception, for cars: New ones' timing is computer-controlled... higher octane can produce a bit more power, but this is because the timing is automatically advanced. I doubt there is an off-road vehicle out there (yet) with this much sophistication.

Save your money... not needed.

  • qadsan

Posted August 07, 2002 - 07:54 AM


Yes, definately save your money. Even Bruce Ogilvie (Honda's legendary Baja racer) has said that a stock XR650 will run better on pump gas than a high-octane race fuel and that all the gas in the Honda pits is Chevron 92- or VP 93-octane unleaded.

If by chance you're using Avgas (Aviation Fuel) as some people classify as racing fuel, make note that its specifically designed for the crtical needs of small aircraft, which requires a more cleaner fuel with different vapor pressures, faster buring, lower fuel density, different boiling & ignition points, etc, and is specifically designed to be run in a low oxygen, low pressure, low temperature atmosphere and typically on low RPM engines. A gallon of Avgas will weigh slightly less than a gallon of pump gas at your local gas station and this was designed into the fuel on purpose to help reduce the weight in aircraft among other things.

There's different grades of Avgas such as 80/87 also known as "Red" for its color and this stuff should never be used in a car or motorcycle because it has low mon octane number of about 80. Then you've got 100/130 also known as "Green", but has a ron/mon octane number of over 100 and contains led. Then there's the 100LL and the LL means Low Lead compared to the stuff it replaced and is also known as "Blue", but it probably contains at least as much and possibly more lead than the normal leaded automotive gasoline we were once used to. Then there's 115/145 known as "Purple" and this stuff is real high octane and was secretely developed originally for fighter aircraft in WWII.

Avgas octane is also rated on a different scale than your normal automotive pump gas and what's 100 octane for Avgas isn't necessarily 100 octane pump gas. Avgas also doesn't burn as hot as pump gas, (there are less BTU's in Avgas) and it leans out your engine, so you should ideally rejet your carb if you plan to use Avgas to get the most out of it or you might actually be loosing power instead of making it.

  • ossagp1

Posted August 07, 2002 - 08:06 AM


I have one engine that is very high on compression that requires race gas. In it I run straight Trick racing gas. It is jetted for it and starts as well as can be expected. My son borrowed some, and I think he would only use it as a last resort. He said the same thing about starting. If you were jetted on the lean side it may actually aid starting, but for the most part I think you should not use it on an engine designed to run on pump gas.

  • xzvs

Posted August 07, 2002 - 04:04 PM


While on the subject of fuel. I have the big bore kit on my 88 xr 600. Previous owner used a 50/50 mixture of racing fuel and 93 octane from the pump. He said straight 93 is probably ok. My question is, should I just run 101 octane? There is a place here that sells it at the pumps (we have a huge classic hot rod community here). Was kinda thinking that is probably bout the same as the mixture he was using. What do you guys think?

Related Content


Fell Off Trailer by usafxr

Dirt Bike   Make / Model Specific   Honda   XR600/650
  • Hot  43 replies

ignitech programmable XR650L CDI by brianhare

Dirt Bike   Make / Model Specific   Honda   XR600/650
  • Hot  47 replies

Post Apocalypse, ThumperTalk style! by Justin Pearson

Dirt Bike   General Dirt Bike Forums   General Dirt Bike Discussion
  • Hot  35 replies

Engine Loping/Sputtering by tcaldwell

Dirt Bike   Make / Model Specific   Honda   XR600/650
  • 2 replies

Which thumper motor for a street tracker? by woz

Dirt Bike   General Dirt Bike Forums   General Dirt Bike Discussion
  • * * * * -
  • Hot  29 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.