Fuel Grade Question?

[mplaydon]

Can anyone tell me what grade of gas I should be using for my 1971 Johnson 50. I know that the oil mixture is 50:1 but it just struck me that I do not know the fuel grade to use. I fired the engine up for the first time in 4 years the other day, after replacing the plugs, impeller cleaning the carb and doing all the usual checks and she runs in idle just great on the muffs. But now I have got to thinking that maybe I used the wrong gas grade. Can anyone put my mind at ease. I used standard 87 grade.

 

[ED21]

Re: Fuel Grade Question?

As far a I know, all stock outboards run on regular gas. The OMC manual allows for alternative fuels with certain percentages of methanal or ethanal, but don't recommend it.<br />I've never put anything other than regular in my OMC outboards.

 

[ob]

Re: Fuel Grade Question?

87 octane is what most use and you will see no improved performance using any higher.

 

[mplaydon]

Re: Fuel Grade Question?

Thank guys I feel better now.

 

[AUGIDAWG]

Re: Fuel Grade Question?

If higher octane fuel burns slower, then wouldn't it work better for someone who does mostly trolling? (timing is more retarded at an idle, requiring less octane, but piston speed is way less than say half throttle, requiring more octane)

 

[DJ]

Re: Fuel Grade Question?

Most outboards do not recommend anything higher than 87 octane.<br /><br />The slower burn rates of higher octane fuels actually hurt outboards. The slow burn causes carbon build up in combustion chambers and ring lands. A sure, yet slow, death for an outboard.

 

[ED21]

Re: Fuel Grade Question?

Does high octane burn slower or does it have a higher flash point so it doesn't detonate under the higher pressure of high compression engines?

 

[willxuout]

Re: Fuel Grade Question?

Let's not go down this road again...there are plenty of long discussions about fuel grades and how they effect performance.<br /><br />Do a search for octane and grab a cup of coffee...this will take a while.

 

[ED21]

Re: Fuel Grade Question?

Just wondering. I use regular gas anyway. I promise not to mention 2 cycle oil.

 

[jim dozier]

Re: Fuel Grade Question?

Augidawg as per the trolling issue, that why the ignition timing is variable - retarded at slow engine speeds and advanced at high engine speeds.

 

[sparkroost]

Re: Fuel Grade Question?

I know recently from experience that some outboards(high compression) MUST have premium gas. No, it's not better for performance! I think is most tests you will find that lower octane produces more power due to better combustion(2 stroke). More fuel is wasted using premium because it doesn't fully burn in a 2 stroke. Lower octane fuel burns hotter and more complete. There are the same additives in 87 as 93, just the quantity is different. I think you may see more carbon deposits due to non-complete combustion and the inefficency of a 2-stroke cycle.<br /><br />Most high performance outboards that have high compression MUST run high octane(140psi+ compression), the manufacturer of your outboard states the fuel and ratio to be used.<br /><br />I own a V4 evinrude and I must use 93 octane and a fuel additive, or a mix of 110 and 93. If I don't, I have to reduce timing 4-6 degrees to compensate. My compression is 160psi.