what octane to use

[brian3127]

i have a 1975 or 6 40 horse. i have been putting the cheap gas in it and it seems to run rough. then when i stored the boat for the winter i put stable in the tank. last year it ran so good i started to think that maybe the stable helped the gas. so should i go with this mixture everythime i fill the tank or go with a higher octane gas.

 

[tashasdaddy]

Re: what octane to use

87 octane, mixed 50:1 TC-W3 outboard motor oil, then add Seafoam, it is better on the motor than stabil.

 

[Vic.S]

Re: what octane to use

See http://www.evinrude.com/en-US/About.Us/FAQ/Oil.Fuel.htm#Q4

Don't use stale gasoline. If you must store it from one season to another add a fuel stabiliser and store full cans only (to minimise the exposure to air)

I prefer metal cans to plastics cans as to a small degree polyethylene is permeable to oxygen. They also exclude light which may also be a factor in the deterioration of gasoline. Store in a cool place too.

Maybe also possible that plastics allow the loss of lighter fractions from the gas.

Before using stored fuel I find it advisable to filter it and to mix about 50:50 with fresh fuel.

Stored my fuel in this way from one season to the next for many years without problems but I do not know if the high ethanol content fuels will keep as well.

 

[Silvertip]

Re: what octane to use

People and technicians blame ethanol for lots for lots of things but in most cases it is an excuse for not actually diagnosing a problem. The key to storage of fuel is to not simply dump Stabil, SeaFoam or any other product in the fuel and expect the engine to run normally in the spring. While adding these stabilizers is recommended, you need to actually run the engine to get that mixture into the engine BEFORE you store it so the fuel system is protected during the lay up period. We've used E-10 since 1997 up here in the midwest and layup is not a problem if the fuel is treated and the engine run before lay up. Adding this stuff in the spring will not bring bad fuel back to life. Your engine will run just fine on plain old 87 octane regular grade fuel (E-10 or not) although ethanol does attach old rubber and some plastics that were designed many years before ethanol blended fuel became available. If you are in an area that just switched to E-10 you are advised to replace all hoses, change the filters and clean and rebuild the carbs to "prevent" any issues rather than having issues after the switch.,

 

[5150abf]

Re: what octane to use

Octane is an anti knock rating, knock is actually preignition, the hihger the octane rating the more resistant it is to preignite.

High octain is required for high compression engines, 2 strokes are pretty low compression and not very prone to preignition.

It however has NOTHING to do with how much power the gasoline yeilds, the only thing it will do is drain your wallet faster.

As TD said, regular unleaded mixed at 50:1 is fine.

If you want your mortor to run its best just make sure your carbs are clean and the plugs are correctly gapped and clean.

 

[Mas]

Re: what octane to use

Also, if you end up storing your gas at the end of the season, it's probably best to top off the tank. This will cut down mixing with air.

MAS