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Old 29 January 2010, 16:24   #11
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Are they the same engine?

Hi Hoggy...

I had a mercury 50 p 4 stroke carbs (1998). I think I was told /remember hearing that this was a rebadged Yamaha unit (someone like outboard tech could possibly confirm?)

The OB had problems after i sold it (it ran fine on muffs, but lost power under load...had new owner baffled).

I think it was Dave 'Wavelength' who reported that he had owned an OB which had had the same problems and that a common fault on these outboards was a cheap rubber water seal which sits at the base of the powerhead. It degrades /expands with age and causes problems. I spoke to another OB mech at the time who said the same from our initial discussion. He was then engaged to change the part...problem sorted.

Obviously this doesn't work if the Yam /Merc aren't the same, but thought it might be worth 'throwing in'.

If it is this problem, the good news is that the seal costs a few quid, but the bad news is that the engine has to be stripped down to reach it.

Sorry if this is a red herring...

Dan
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Old 29 January 2010, 17:47   #12
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Country: UK - England
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Boat name: Reel Action
Make: Shetland
Length: 5m +
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Excellent help guys ... I will seriously be following all your suggestions ... I do have a compression tester and a fuel pressure tester. I have looked at the diaphragm on the fuel pump and it visually appears ok.

I have noted the fuel filter bowl is full and clear when this problem occurs. I am off this week on holidays and as luck has it, I have been ill, in bed for the last 3 days. Hopefully I should be ok in a day or so (just when my holidays finish) it might be a good idea that I am virus free before I get back to work seeing as I am an Emergency Medical Technician lol ... I intend on giving it a good looking at, and getting it out on the water.

A couple of years ago I had a similar problem with the engine though not identical, and that took some solving. It turned out to be a snapped exhaust pipe that had dropped down blocking the exhaust passage, causing backpressure! ... as the boat was bouncing around at times it would dislodge itself and run ok, till it happened again ....

Of course, I have already dropped the leg to make sure it hadn't happened again lol

Don't yea just love it when your outboard starts playing up .. I need a lottery win
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Old 30 January 2010, 05:55   #13
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Quote:
Originally Posted by Hoggy View Post
Don't yea just love it when your outboard starts playing up .. I need a lottery win
Lottery numbers for Saturday... 5, 12, 13, 17, 43, 49 and bonus ball 22. If you win - give me 50%!

As Barry (outboardtech) mentioned, have a look at the thermostat, and the housing recess itself. Not uncommon for it to salt-up.
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Old 31 January 2010, 05:15   #14
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Originally Posted by spartacus View Post
Lottery numbers for Saturday... 5, 12, 13, 17, 43, 49 and bonus ball 22. If you win - give me 50%!
Got the bonus ball right!
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Old 01 February 2010, 12:42   #15
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Can't help with the lottery numbers, sorry.

Have you tried pumping the priming ball while the problem is happening? Correction of the problem would point to a fuel delivery issue.

A buddy was having very similar issues with his Merc 60 4-stroke; found it ran fine when pumping the ball at upper revs. Turned out some plastic bits from a deteriorating fuel tank had gotten to the engine (no water separator), put a hole in the low pressure fuel pump diaphragm and took out the high pressure injector fuel pump. With carbs, you don't have to worry about an HP pump (good thing, as it was about $400.)

Luck;

jky
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Old 03 February 2010, 12:36   #16
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Country: UK - England
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Have tried new fuel line/priming ball plus different fuel tank/fuel etc ... problem still persists!
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Old 05 February 2010, 15:15   #17
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Hoggy have you done the TEST'S I posted too you . PLease would LIKE the result's of these test's .Fuel pressure etc etc . cheers
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Old 05 February 2010, 22:11   #18
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Not as yet mate ... I've been on nights dragging in all the drunks off the streets, or so it would seem lol ... I'm hoping to get the boat out Sunday (would have looked at it Saturday, but it's the six nations) ... as soon as I find anything. I will post ;-)
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Old 15 February 2010, 20:16   #19
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Managed to spend and hour or so looking at the engine today, what with work commitments it was the soonest I could get round to looking at it.

Carried out a fuel pressure test and it was “on average” 3psi.

Have decided to replace the thermostat, haven’t tested the old one but at least it will rule out it be a cause of our problem.

Going to get it out on the water sometime next week … my problem is I’m an Ambulance man and my mates a Fireman and its getting our shift to coincide.
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