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Old 27 February 2021, 15:07   #1
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Country: UK - England
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Boat name: 154
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Engine: Mercury 7.5 lightnin
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Intermittent missing, sluggish pick up and periodic water spray- what next?

First time out from the workshop for my mariner 15 hp 2 stroke circa 1980. Stays and ticks over with tweeks to idle screw. Lot of smoke but the whole thing was fogged over the wind overhaul.

Anyway, the mix is rich as the new plugs are black. It has issues;

Feels sluggish on revs and it wants to give more but feels only 70% there.

The water outlet blows lots of air( after new impeller) and just sprays some water out in cycle of none, then a blast, etc. There lots of air hitting the water below but no constant pee etc.

There is associated Iím sure, a periodic FUTT pressure and noise after say 10 seconds of cycle. This coincides with the water spray sometimes I guess.

Iíve revved it up quite a bit a nd it seems to go away but again itís sluggish on pick up.

Can leave it tick over for ages mind.

Iíve changed;
Impeller
Cleaned the thermostat housing and new gasket. ( itís not over heating)
Put some wire up the water outlet to free crud.
New plugs
Pressure test today on warm was 100 on both once warm.

What or how can I tweak to make it as smooth as considering this is an engine of the past that has done very little miles.

Much respect to replies.

Dai
I can send videos.
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Old 27 February 2021, 15:13   #2
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Blocked main jet in the carb. Water I suspect you have no seal since fitting the impeller so no pressure
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Old 27 February 2021, 15:23   #3
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Quote:
Originally Posted by neil.mccrirrick View Post
Blocked main jet in the carb. Water I suspect you have no seal since fitting the impeller so no pressure
Ah so I will clean that carb and jet out. I did not replace the gasket on the new impeller.
Are there things I should do there regard sealing it right up?
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Old 22 March 2021, 18:22   #4
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Quote:
Originally Posted by neil.mccrirrick View Post
Blocked main jet in the carb. Water I suspect you have no seal since fitting the impeller so no pressure


Hello Neil.
Just picking up on this again.
Iíve got the two new gaskets to change over and I see there is a rubber seal in the housing to meet the water pipe but when in gaged is appears to be a little short owing to the tapered angle of the metal water pipe. Perhaps it a perfect fit but should I add some non hardening sealant to this connection to make sure it works without any air intake at that point.?
I was also thinking of adding gasket sealant to both gaskets to make sure that area is tight as.....
Any tweaks recommended?

Had the cab off and cleaned again but still a Ďfuttí now and again.

Am going to clean it once more. Is sonic the only way or is carb cleaner and air sufficiently ok?

Cheers
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Old 23 March 2021, 02:49   #5
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The gasket should be fine if itís an OEM part. The taper is to ease fitting. Re that carb sonic is the best way but I have used white vinegar with good results. Leave parts in overnight
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Old 23 March 2021, 17:30   #6
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I'm confused regard the water pressure.


Testing everything - With the lower unit and pump assembly off I put a hose pipe up and down the lower intake - good flow.

but with he engine horizontal on it back and the hose pipe on the tapered pipe, up into the leg , the engine fills up with water then flows out back down under the tapered pipe and out of the exposed inner leg.
I cannot get it to emerge from the normal pee hole outlet.
Is this a pressure cycle thing to make that happen when all lower outlets are sealed off?
Does it matter if the thermostat is in or out at this stage of flow check?

I will take it out and see if it comes out of there in a good flow I guess before being forced to exit thru the pee hole.

Does water also run back down the leg normally as well ?

In prior runnings when all assembled, the pee outlet just sprayed a powerful spray mist fan like a garden hose gadget in time with the firing cycle.
What is the correct appearance of water out of the top engine?
Pee or spray?
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