I've been told by a knowledgeable Mercury mechanic that I should run ONLY white gas, 93 octane, in my 2 cycle Mercury motor; only AMACO, EXXON, or BP. He made convincing arguments (non-white gas has various additives that will cause problems..). Recently I was told that you should NEVER run white gas in a 2-cycle engine with equally convincing arguments (white gas has water in it and alcohol is added to dry the water which causes the mixed oil in a 2-cycle application to separate from the gas). Who is right? Here’s my setup: 1996 Mercury 225 ProMax with Bobs high performance exhaust, Sport Master Gear case, Boysen Reeds, 2.5 Carbs, dyno at 245HP, on a 10" Rapid Jack Plate. Turning a 27 DAH SRX to 7000 at 86.2 mph (gps).. It's pretty hot so I don't want to invite trouble.
Howdy, Bud.Both of your know-it-all advisors are wrong.Any unleaded, alcohol free gasoline over 86 octane is safe to run in your engine. The additives in premium fuels are more likely to help than harm, EXCEPT for alcohol. If your Merc is a tower of power 6, many people recommend premium fuel.I personally prefer to run 87 octane in my Suzuki DF 70 4 stroke, but OMC recommended premium for my Johnson 9.9 4 stroke. Both of these modern, 4 stroke engines will tolerate up to 10% Ethanol or 5% methanol.Good luck.