70hp merc busted

[duckhunter55]

Just bought a 1980 70hp mercury 3 cylinder 2 days ago and ive already ruined it. Bought it from a retired boat mechanic who holds over 40 diplomas from factory outboard motor schools. Motor had 140 lbs compression on all cylinders and he had just replaced water pump and decarboned within the last 2 weeks. Put motor on the boat and took out. Motor started and ran fine for about a mile when rpms start going down and it slows way down and cuts off. I took off the cover and felt the head and it didn't even feel warm so i knew i didn't over heat, but we finally got it started back and puttered home. At the ramp i checked compression and top cylinder had 40lbs of comp. and the others still had 140. Poked weer eater string in pee hole and about an inch of mud came out. My question is would the pee hole clogging up cause it to over heat? and why weren't the other cylinders affected. I remember looking back and seeing spray coming from the rear and thinking that it was peeing. We also ran it on the muffs when we got back and it pissed water strong and was coming from the 2 port holes and thru the prop.

 

[Laddies]

Re: 70hp merc busted

No a plugged telltale won't make a engine overheat 95% of the water goes down the exhaust. I would get a hold of the seller ASAP and see what he says. Running on muffs will not tell if the w/pump is really working properly because the muffs pressurize the system to a point but it does sound like the engine starved for water, it might have a popit valve that's stuck or a bad thermostat depending on the year of the engine.

 

[CharlieB]

Re: 70hp merc busted

Or the upper carb went lean, either dirty or a weak fuel pump not completely filling the top carb.