Don't use 'premium' fuel in outboards!

[sam_uk]

So this weekend I stuck some http://www.seafoamsales.com/ in my old 1990 7.5hp mariner. One cloud of white smoke later the engine was running lovely, the rough idle was smoothed, it started first time (rather than the more usual fifth).

I then re-fuelled it and the trouble started, it would only run at fantastically high revs for about 30 seconds and then die.

Cue new spark plugs, taking carburettor apart, scratching head, swearing, putting carburettor back in, cursing crappy Seafoam, taking carburettor apart again, more swearing, breathing clouds of 2stroke fumes, more swearing..

Eventually I figure out that without paying too much attention I had put 'premium' fuel in it. Which it doesn't like at all. I put some 'standard' fuel in it and it runs like a dream.

So things I learnt;

1) Seafoam works great

2) Only put bog standard fuel in old outboards.

 

[Lakesailor]

I can't see the connection.

it would only run at fantastically high revs for about 30 seconds and then die

Sounds more like an air leak which you may have cured with rebuilding the carb etc.

 

[sam_uk]

Definitely the fuel

The fuel change took place after I had been trying the 'premium' fuel, the carb stayed in between the 'premium' and 'standard' fuel

'Premium' fuel has a higher octane rating, which means it combusts more easily. This evidently did not agree with my outboard. It may be fine in newer/different models.

 

[VicS]

Seafoam is very popular additive for outboard fuels in the USA. I have never seen a UK supplier. Where did you get it?

Like LS I am very surprised that the higher octane fuel caused any trouble. Usually just considered a waste of money for a two stroke

 

[sam_uk]

Seafoam;

http://shop.ebay.co.uk/?_from=R40&_trksid=p3907.m570.l1313&_nkw=seafoam&_sacat=See-All-Categories

 

[VicS]

Thanks. But what a price. $6.99 in the States

 

[mikefleetwood]

'Premium' fuel has a higher octane rating, which means it combusts more easily.

I'm no expert, but I think that, if anything, the opposite is true - Higher octane fuel contains a greater proportion of some retardent (used to be lead?) to reduce tendency to pre-ignition in higher compresion-ratio engines.

 

[sam_uk]

I'm no expert, but I think that, if anything, the opposite is true - Higher octane fuel contains a greater proportion of some retardent (used to be lead?) to reduce tendency to pre-ignition in higher compresion-ratio engines.

You are quite right, I just checked. I guess that makes more sense

 

[Poignard]

Not one of my better ideas

Talking of o/b motor fuel reminds me of a stupid thing I did years ago.

I had sold one outboard and, on the way to the boat the following weekend, I bought a new one but had no fuel with me for it. I was planning to row out to the boat from the club pontoon, knowing I had petrol on board.

There was a bloke at the club pontoon unsuccessfully trying to start his old outboard to get out to his yacht; he had a can of petrol with him.

Ever helpful me says - " why don't you give me some of your petrol for my new outboard and I'll tow you out to your boat"

Result: two outboards out of action due to dirty fuel.