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Old 13-07-2014, 08:21 PM   #1
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Country: UK
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Boat name: Isabella / Cool Runnings II / Bella / Sea Pup / Sea Dog / Speedy II
Boat make: Colvic 35 Suncruiser / Phantom 16 / Zodiac 420 YL / RIB / Apollo 9
Engines: 2 x Perkins Sabre 225ti / Mercury Pro XS 115/ Tohatsu 2.5 / Mercury 25 / Mercury 50
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Engine trouble

Hi everyone,

Not sure if you can shed any light on this but if you can that would be great.

I have a Carbed Yamaha f100a. I went to go out a the beginning of the season and it would tick over fine but would not rev up. Checked compression and spark all good so had the carbs cleaned by a local engineer (sonic cleaner) all put back on carbs balanced and the boat worked since Easter. put in new spark plugs and changed fuel filter.

I was out yesterday all running well, then when coming back in and slowing to 5 knots, the engine spluttered and stalled. The only way to start it was nearly full revs. As so as you drop the revs to idle it would stall. If I reved up and got it into gear in time boat would run flat out no problem. But as soon as the revs dropped it would stall again.

I have tried cleaning the jets and fuel filter but still no joy, any ideas please?

Many thanks

Stewart
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Old 13-07-2014, 11:03 PM   #2
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Country: Ireland
Location: Dublin
Occupation: Boatbuilder
Boat make: Hydrostream V-king, 650SS OCR ,Ring 21, Ring 18, Phantom 18.
Engines: 300Hp Mercury 2.4, 130 Yamaha, Bridgeport EFI, XR6, Merc 200.
Cruising area: Malahide, Dublin

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Bump the choke as its about to stall, if it springs back to life strip the carbs as low speed circuit is blocked.

Also try draining the carb bowls, could be water in them.

Sounds like its fuel related!
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Old 13-07-2014, 11:04 PM   #3
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Country: Ireland
Location: Dublin
Occupation: Boatbuilder
Boat make: Hydrostream V-king, 650SS OCR ,Ring 21, Ring 18, Phantom 18.
Engines: 300Hp Mercury 2.4, 130 Yamaha, Bridgeport EFI, XR6, Merc 200.
Cruising area: Malahide, Dublin

Join Date: May 2004
Location: Dublin
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Also check new fuel filter is on tight and check fuel line for air leaks.
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Old 13-07-2014, 11:07 PM   #4
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Country: UK
Location: Leigh-on-sea
Occupation: IT Director, www.lighthouseit.co.uk
Interests: Boats, Surfing & Snowboarding
Boat name: Isabella / Cool Runnings II / Bella / Sea Pup / Sea Dog / Speedy II
Boat make: Colvic 35 Suncruiser / Phantom 16 / Zodiac 420 YL / RIB / Apollo 9
Engines: 2 x Perkins Sabre 225ti / Mercury Pro XS 115/ Tohatsu 2.5 / Mercury 25 / Mercury 50
Cruising area: Thames Estuary / River Crouch / Salcombe

Join Date: Jun 2004
Location: Leigh-on-sea
Posts: 918
Quote:
Originally Posted by Hydrostream View Post
Bump the choke as its about to stall, if it springs back to life strip the carbs as low speed circuit is blocked.

Also try draining the carb bowls, could be water in them.

Sounds like its fuel related!
Thanks for response, I drained the carb bowls no water, will try the choke trick and run off another tank / line in the morning.
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Old 14-07-2014, 10:10 AM   #5
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Country: In the UK, in an offfice, looking out the window at the rain.
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Boat name: DoubleSix
Boat make: Ring 21c
Engines: Opti 200
Cruising area: Lyme Bay

Join Date: Aug 2012
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I had identical symptoms many years ago with a blue band merc 50 (yes, that long ago). Turned out to be a corroded water jacket on the baffle plate at the exhaust outlet port.

What was happening was that at tick over the exhaust pressure was not enough to overcome the water leak pressure and water was being directed through the exhaust port in to the cylinder, thus causing the poor running/misfire/stall.

if you managed to get the revs up, the exhaust outlet pressure overcame the leak pressure and the engine ran virtually normally.

The worst thing i did was to switch it off, put the boat on the trailer for a few weeks while I thought about what to do, as the water that got in to the bore seized the engine solid. Ended up having to strip the engine right down to just the block and one stuck piston (main bearings and crank removed). Knocked it out with a hammer and wooden block, it was just gummed up with salt, amazingly there was no cylinder or piston corrosion. replaced the baffle plate and it ran perfectly.
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