When you pull up to a gas pump on your motorcycle the main decision you’ll need to make is which octane rating of gasoline to use.
Your options will vary slightly depending on the gas station and your location, but you’ll usually have 3 options ranging from Regular (lower octane, 85-87) to Premium (higher octane, 90-93).
Is there a hard rule of thumb that you should only use premium, high octane gas in your motorcycle? No, it depends.
The first place to look for this answer is your motorcycle owner’s manual, under the seat, or on the gas cap. Your motorcycle manufacture will specify the recommended octane rating for your bike.
The simple answer is this:
- Engines with a higher compression ratio require a higher octane fuel.
- Engines with a lower compression ratio require a lower octane fuel.
Using the wrong type of gas in your engine can cause performance issues including:
Motorcycles with high compression ratios use higher octane fuel.
Motorcycles with lower compression ratios can use regular fuel.
Using a higher octane fuel will not make your motorcycle faster or more powerful.
A newer Harley is going to take premium, while your 70s-80s Honda or Kawasaki is probably fine with regular gas.
Differences Between Octane Ratings
The fuel in your motorcycle can be ignited by a spark, a heat source, or through compression.
A combustion engine works by compressing the atomized fuel/air mixture in the combustion chamber and igniting it when the spark plug fires. If everything is working properly, the fuel ignites at the correct time, sending power through the crankshaft and to the final drive until you kill the engine.
Octane ratings refer to the chemical makeup of the gasoline.
Higher octane fuels are more resistant to ignition by compression.
In a high compression engine, high octane fuel prevents pre-ignition, which can cause knocking and throw the timing off.
Is Ethanol Gas Bad for my Motorcycle?
Ethanol is found in most gasoline in the U.S. For newer motorcycles, ethanol fuel is not an issue.
However, older bikes can experience some problems associated with ethanol gasoline.
Ethanol fuel has a shorter shelf life, and can cause your older carburetors to gum up with varnish and gunk. It can also have negative effects on hoses, gaskets, and seals.
If gasoline without ethanol is available near you, you can use that (E0).
Otherwise, certain fuel additives can help prevent gunk and build up. Riding the bike and starting it regularly can also help curb some of the negative effects of ethanol gas.
How Long Can a Motorcycle Sit Before Gas Goes Bad?
Gasoline that has been sitting will typically go bad within 6-12 months.
Motorcycles are more susceptible to bad gas than cars or lawn mowers.
If you have bad gas in a can, you can usually add it to your car or lawn mower. If you have bad gas in your motorcycle tank or carbs, you should drain it.
What Happens When Gas Goes Bad?
Bad gas in your motorcycle has a tendency to gum-up and varnish.
If you’re working on an old motorcycle, this is the brownish-tar substance you’ll find in the carbs.
Motorcycles that have been sitting too long will likely need a full cleaning of their carburetors.
How to Drain a Motorcycle Gas Tank
If you’ve got bad or old gas in your motorcycle, or plan on working on the tank, you can drain the gas.
The easiest way to drain the gas is directly from the hose from the petcock or fuel valve.
To drain a motorcycle gas tank:
- Turn the petcock to the off position.
- Disconnect the fuel hose(s) at the carb.
- Route the hoses to a fuel container.
- Turn on the petcock to the reserve position.
- Drain the fuel.
Be sure to drain the fuel from the carb’s bowls as well.
After draining your gas tank you can prepare it for storage or remove rust from the tank.