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Old 19 July 2015, 18:43   #1
Country: UK - Scotland
Town: Scotland
Boat name: Barry
Make: Avon
Length: 4m +
Engine: 50hp Mercury
Join Date: Jul 2015
Posts: 6
Mercury Outboard Engine fire

Hello, New to the world of ribbing, family history of boats and water borne activities and I've decided it's my turn.

I have a 4 meter Avon rib. It has a Mercury 50 thunderbolt 2 stroke outboard on it. Today, arrived at the slip, boat into the water. I noticed I had driven the 6 miles to the slip with the fuel line attached to the tank. I then primed the fuel just until the bladder went hard.

Fired up the engine, then boom. loud explosion, not enough to blow casing off etc, however a small fire started. It was quickly extinguished with a powder extinguisher.

Boat out of the water and returned home.

Carbs and bottom end cleaned out of powder. Primed fuel and engine fired up no problems.

Obviously the explosion was due to fuel from somewhere. I checked for leaks - none.

I did noticed the engine had two cards and no air filter? Is this right, direct air entry?

Can anyone offer advice. Has the fuel been primed too much and as a result there has been excessive fuel which has leaked out the entry to the carbs and in turn starting the fire?

Any advice would be gratefully received.


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Old 20 July 2015, 01:08   #2
beerbelly's Avatar
Country: UK - England
Town: teesside
Make: osprey eagle and sr4
Length: 3m +
Engine: yamaha 130 mercury40
Join Date: Apr 2014
Posts: 601
it could be one of your carbs is overflowing the needle valve in the float chamber can get a bit of crap in the seat and stay slightly open this sometimes does not always happen but it will cause the carb to drip and maybe the flooded carb caused a small backfire when you fired it up (excuse the pun)

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Old 20 July 2015, 01:10   #3
Country: UK - England
Town: Sheffield
Boat name: Touch Bottom
Make: Avon
Length: 4m +
Engine: 50 hp Merc Power t&t
Join Date: Jul 2008
Posts: 230
Hi, you will get some fuel leakage/spillage under the cowl with squeezing the bulb, I always do, but it still needs a spark to ignite it. It may be a good idea to have a good look at your spark plug leads make sure they are in good order and tight, check for cracks in the insulation and make sure there are no bare wires anywhere that could cause a spark. As for the air filter, there should be a strip of foam rubber around the front cover, this is the air filter. hope this helps..
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Old 20 July 2015, 02:02   #4
spartacus's Avatar
Country: UK - Scotland
Town: Aberdeenshire
Boat name: Sula
Make: Ribcraft 4.8m
Length: 4m +
Engine: Tohatsu 60hp + aux
MMSI: 235087213
Join Date: Jun 2007
Posts: 3,055
Get this checked out professionally. In 30 years of boating I've never (touch wood) had an outboard catch fire, and I've had some old motors before. It's one thing having a small fire on a slip, quite another at sea.

With the cowl exposed, where exactly was the fire on the engine, and what damage was done?

The carbs would be the first thing I'd look at, followed by HT leads, fuel and vacuum hoses, the fuel pump and then the wiring, including chaffed or exposed cable.

If you're looking for a replacement engine, here's a few long-shafts 50hp engines:

Second Hand Archives - West Wales Marine

Buy Used Outboards tohatsu 50hp power trim, oil injection, long shaft 50.0HP Outboard at Bill Higham Marine

Good luck with this.
Is that with or without VAT?
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Old 20 July 2015, 03:42   #5
Country: UK - England
Make: Humber / Phantom
Length: 5m +
Engine: Lots of Yamahas
Join Date: Feb 2006
Posts: 113
Here's what can happen with a fuel leak!

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Old 20 July 2015, 03:54   #6
1eyedjim's Avatar
Country: UK - England
Town: Birmingham
Boat name: Sparrowhawk
Make: Osprey
Length: 5m +
Engine: Yamaha 90hp 2T
Join Date: Apr 2010
Posts: 212
few gaskets and a t cut and that will look like new
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Old 20 July 2015, 14:58   #7
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Poly's Avatar
Country: UK - Scotland
Boat name: imposter
Make: FunYak
Length: 3m +
Engine: 2 stroke YAM 20 HP
MMSI: 235089819
Join Date: Sep 2005
Posts: 9,416
Originally Posted by 1eyedjim View Post
few gaskets and a t cut and that will look like new
It will be on ebay with the line - "not running, but just needs a service"

Originally Posted by mercury
Hi, you will get some fuel leakage/spillage under the cowl with squeezing the bulb, I always do,
is that normal? I've never noticed this - it doesn't sound right to me.
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Old 20 July 2015, 16:49   #8
Festinghouse's Avatar
Country: UK - England
Town: Chorley / Holyhead
Boat name: Northwind Challenger
Make: Tornado
Length: 6m +
Engine: Force/Mercury 120
MMSI: 235080598
Join Date: Jun 2011
Posts: 1,379
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no shouldnt leak from priming - thats what float valves are to prevent. my force with tilotson carbs spills a small amount of fuel out of them when the engine is tilted up - a problem im currently trying to resolve
"Life may often suck, but the alternative is unacceptable"
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Old 20 July 2015, 23:57   #9
Country: UK - Scotland
Town: Denny
Boat name: Hebridean Storm
Make: Coastline
Length: 6m +
Engine: Honda 130hp
MMSI: 235107505
Join Date: Mar 2013
Posts: 500
I'd be surprised if most carburated two strokes don't spill a bit of fuel into the tray now and then. I'm yet to pull a cowling off one and not get that familiar "wiff". The 6hp Yam I had was the only one that actually caught fire (put out) and I traced that to a bent cowling bracket that an HT lead was arcing over to. Sorted bracket and replaced HT lead.
So I'd look for the ignition source because you're never going to guarantee there'll be no petrol fumes under the cowl.
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Old 22 July 2015, 01:33   #10
Country: UK - England
Town: Midlands
Make: Ribeye 600
Length: 6m +
Engine: Yamaha F115
Join Date: Dec 2010
Posts: 203
Worn Neddle / seat in the carbs can allow fuel to leak past when the tank has pressure caused by expansion.

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