You ask we answer. Here's the latest in our "Ask a Mechanic" series.
Q: What kind of gas should I use? I just grab the cheap 87 octane from the pump on my way to the track. That good enough?
A: Great question and one we get a lot. Yes, it's good enough but depending on your bike you might want some higher octane fuel. Regular 87 octane pump gas works fine on fuel-injected 4-strokes but on a 2-stroke the best gas would be an ethanol-free 92 or 93 octane because the lower octane tends to cause the engine to detonate which sounds like pinging or knocking. (Depending on where you live 92 and even some places 91 is the highest octane available.) Whatever gas you use, ideally, a non-ethanol blend is preferred but it's hard to find nowadays. Regardless don't ride more than 10 percent ethanol-based fuel.
Some riders insist on race gas which costs quite a bit more and unless you're a pro, race gas won't do you a bit of good. Most weekend warriors and even casual racers don't have the set up or skills to squeeze the extra bit of power and performance racing gas provides. So stick with the 87 in your 4-stroke and the higher octane for your 2-stroke and save your money for spare parts.
One thing to consider is whether you have done any engine modifications like advanced timing and increased compression that requires a higher octane fuel to prevent the knocking and pinging. Then try the extra octane at the pump.
For more information on the best gas to use in a dirt bike or ATV engine check out "87, 89, 92 or Race Fuel - What Gas to Use in Your Dirt Bike or ATV."