What type of fuel should I run in my Mercury 1992 100HP 2+2 outboard, in Australia?

Question

I have been running BP Ultimate 98(octane) but after reading some reviews on other sites it seems as though this may have repercussions down the track, i.e. carbon buildup, piston burnout etc. There also seems to be some confusion with the ratings of fuel between the US and OZ and which is the correct one. I recall reading the manual a long time ago and it stated that anything87 octane or higher is suitable but am unsure whether or not 98 Octane fuels would have been available in 1992 when the engine was made. Also as it is a 2+2 engine (oil injected) is it OK to disconnect the fuel line and run the fuel out when flushing? I have noticed that when I have emptied the carbies there is only fuel in the bottom 2 carbies, how can I combat this without flogging the engine on Cool-down (flush). Are there any issues with leaving this fuel in the carbies for a few month at a time and should I be taking the fuel line off at all if it is Oil injected? Any advice appreciated.

Answer 1

You shouldn't have to worry about the fuel. You need to keep your eye on the oil you use. Use the best low ash oil you can find.

If you park your boat for an extended period of time, use Sta-Bil. It's a gas stabilizer that works great. I don't know if available there though.

Answer 2

First off gasoline by any other name is still gasoline. 87 octane is regular gasoline by US standards. 98 octane is 5 points higher octane than US high test or premium. The higher the octane, the hotter the gas will burn. Try to find lower octane gas. You don't need 98 or even 93 octane in your boat.

If you are going to leave your boat sit for months at a time get some gasoline stableizer. You should be able to find it where they sell lawn equipment with small gas engines. Or you can buy it online if you can't find it. In the US the top brand name is StaBil. You add it to your tank and run the engine long enough for it to make it to the carbs and then you don't have to worry about draining your carbs.