How long can MR12 be safely left in the gas tank?

While it’s always best to drain MR12 after use, we’ve had no issues leaving it in the tank for up to two weeks—with no fuel pump damage or gumming of the fuel system. That said, MR12 is far more stable than MR9, which we do not recommend leaving in the tank under any circumstances.

Important Considerations:

• Oxygenated fuels like MR12 evaporate quickly through vented fuel caps, which means the power-producing oxygenates can diminish rapidly.

• We’ve seen measurable power loss after just 48 hours if the bike is left sitting with MR12 in the tank.

Extended Testing:

In a controlled test, we intentionally left MR12 in the tank of our 2017 GSX-R1000 for eight weeks with no negative effects. This may be due to Euro 4-compliant bikes having more robust fuel system materials—but this is not a recommended practice.

Best Practice:

• Drain MR12 after each use for optimal performance and fuel system longevity.

• If stored short-term (a few days), try to keep the tank sealed and the bike in a cool, dry place to minimize evaporation.

Still unsure? Contact us with your specific application—we’re happy to help.