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Old 14 April 2011, 16:26   #1
Country: UK - England
Town: surrey
Make: Ribcraft, bombard
Length: 4m +
Engine: Yam 60,tohatsu 3.5.
Join Date: May 2010
Posts: 43
Motor Loosing Power

Been running a Johnson 50hp - 2 stroke acquired recently.
Been running nicely until today when the engine looses power after a few minutes of running and revs drop back to about 3000 rpm and no more power available. Normally run the motor in the sea but last week did run in the Medway. So initial prognosis was overheating caused by blockage in cooling water supply caused by something leafy from the river. Back on land tried cleaning everything out - but no obvious sign of any blockage .

Took motor to local engineer and he checked carbs which look fine . Suggested that mix we were running (50:1) was too rich and should be using a 100:1 mix. The motor originally had an auto mixer that has been removed - and looking at manual it would seem that 50:1 is correct.

Any body any ideas as to what else to check....

Hopefully back on water tomorrow for a test !

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Old 14 April 2011, 16:36   #2
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Country: Ireland
Make: Redbay Boats
Length: 9m +
Engine: 370hp
Join Date: Feb 2008
Posts: 13,849
Have you ruled out fuel starvation?

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Old 14 April 2011, 16:57   #3
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Country: UK - England
Town: The wilds of Wiltshire
Boat name: Dominator
Make: SR5.4
Length: 7m +
Engine: Yam 85
MMSI: 235055163
Join Date: Jul 2005
Posts: 12,880
Don't go back to that engineer!

I'm with willk-prob fuel starvation. I take it you've got a good telltale?
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Old 15 April 2011, 01:43   #4
neil.mccrirrick's Avatar
Country: UK - England
Town: Oldham
Boat name: Miss Isle
Make: Solent 6.9
Length: 6m +
Engine: 225 optimax
Join Date: Jan 2008
Posts: 1,082
I've been having loads of problems like this recently, first thing to check is will it rev when its not under load? So if you are in neutral can you rev the engine? If you can first easy thing to check is, is the tank vented, could be as simple as a vacuum lock.
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