Repair & maintenance: Outboard engine hunting at idle

Outboard engine hunting at idle

Printed From: Yachts and Yachting Online
Category: General
Forum Name: Repair & maintenance
Forum Discription: Questions & tips on the subject
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=13620
Printed Date: 07 Aug 25 at 3:46am
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Topic: Outboard engine hunting at idle

Posted By: Wetabix
Subject: Outboard engine hunting at idle
Date Posted: 01 Jul 20 at 4:57pm

My car idles perfectly, as does my lawnmower and, up to a point, my hedge trimmer, as do most marine inboard engines. Why then does my outboard (Mariner 6HP fourstroke) hunt when at idle and constantly threaten to stop just as I let go of the mooring? Actually it usually keeps going but I just wonder why most small outboards seem to require constant fiddling with to start reliably and run smoothly when in neutral.

Replies:

Posted By: PeterG
Date Posted: 01 Jul 20 at 5:25pm

My Honda 2.3 started hunting at the end of the season before last. I got it serviced and the problem was dirt in the carb. It was put down to old petrol gumming up the carb. Once cleaned it's been fine, and I make sure I add fuel stabiliser these days - and all now seems fine.

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Peter
Ex Cont 707
Ex Laser 189635
DY 59

Posted By: Wetabix
Date Posted: 02 Jul 20 at 6:41am

Thanks for that- what is fuel stabilizer? I had the varnish in the carburettor thing some years ago and have sine been meticulous in running the engine dry at the end of the season. I also fitted a water separator which was a disaster. The diagrams in the service manual are not exactly like my engine but I have managed to adjust the pilot jet and it's working pretty well at the moment, but my Viking lawnmower is better!

Posted By: PeterG
Date Posted: 02 Jul 20 at 11:26am

Google "Fuel Stabiliser", and you get something like this:

https://www.google.com/search?ei=oMP9XteABNuU8gKNjp_ADA&q=fuel+stabiliser+uk&oq=fuel+stabiliser&gs_lcp=CgZwc3ktYWIQARgBMgIIADICCAAyAggAMgIIADICCAAyAggAMgIIADICCAAyAggAMgIIADoECAAQR1CfggFYn4IBYLOMAWgAcAF4AIABU4gBU5IBATGYAQCgAQGqAQdnd3Mtd2l6&sclient=psy-ab" rel="nofollow - https://www.google.com/search?ei=oMP9XteABNuU8gKNjp_ADA&q=fuel+stabiliser+uk&oq=fuel+stabiliser&gs_lcp=CgZwc3ktYWIQARgBMgIIADICCAAyAggAMgIIADICCAAyAggAMgIIADICCAAyAggAMgIIADoECAAQR1CfggFYn4IBYLOMAWgAcAF4AIABU4gBU5IBATGYAQCgAQGqAQdnd3Mtd2l6&sclient=psy-ab

The main market is, I think, lawn mowers - fuel gets left in over the winter etc. So a garden machinery shop would have it, though I tend to buy it online.

I use the Honda one as my OB is Honda. It's supposed to stop the fuel going gummy.

But these days I also always empty the tank and run the carb dry before winter too.

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Peter
Ex Cont 707
Ex Laser 189635
DY 59

Posted By: NickM99
Date Posted: 04 Jul 20 at 3:59pm

Useful thread! I have just had to pay to get an outboard and a mower sorted because of bad fuel. My mower shop is trying to sell me a synthetic fuel (which works well) but costs about £20 for 5 liters. I have now ordered some fuel stabiliser from Amazon.

Posted By: PeterG
Date Posted: 05 Jul 20 at 8:28am

Yes, they tried to sell me expensive artificial fuel after my engine needed cleaning. I reckoned if Honda were prepared to sell stabiliser in their name they probably thought it worked, and went that way instead!

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Peter
Ex Cont 707
Ex Laser 189635
DY 59

Posted By: Wetabix
Date Posted: 05 Jul 20 at 10:29am

Well, wasn't that interesting? Do manufacturers recommend fuel additives? Who ever reads the manuals? Since Molyslip and Redex went out of fashion in the late 60s and Which? panned the more expensive variants of Unleaded I have not bothered. But there are some good articles on fuel stabilizers online mainly to stop the damage American ethylene additives do to boats (like dissolving fuel tanks, it seems!) I shall try some SeaFoam and see what happens. Thanks to all for the pointer.

Posted By: Bootscooter
Date Posted: 06 Jul 20 at 11:45am

I bought a boat with a 50hp Yamaha recently, and while it ran fine, it was occasionally missing and bogged down a bit when accelerating hard.

New spark plugs
new fuel filter
Concentrated Seafoam run through it (and left for 24hrs - then repeated)
Carb cleaner sprayed into the float bowls
Carb cleaner into the intakes while running

.... and it now runs great....no faster, but smooth as you like now.

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Posted By: Paramedic
Date Posted: 09 Jul 20 at 11:17am

These days when ive used the engine for the last time for a while I always disconnect the fuel and let the carb run out. The jets are so fine it doesn't take much to clog them.