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Problems with my 1975 Mercury 40 hp

P

Paulette

Guest
" Hi..we launched our boat thi

" Hi..we launched our boat this year after it sat all last season. It was not "peeing" properly (sorry..don't know the correct term) and was run slowly to our dock. (Maybe 200 yards) We ran a wire down the hole to unplug it and it began to work..running a stream of water about the circumference of a pencil. We ran the boat down the river some and shut it off. When it was restarted...the throttle was siezed up and we had a heck of a time getting back to the dock. Next day...throttle moved freely...boat started right up. Again went a short way ...motor rattled at a low throttle...smelled hot...still peeing a pencil stream but very hot to the touch. Back home we went...almost there...engine dies...again throttle is siezed up. :0 Thank God for oars. Again...engine will restart once allowed to cool..throttle moves freely. We're not dumb enough to go out on the water again.
Any ideas? Paulette "
 
"Paulette,

The throttle is

"Paulette,

The throttle is probably seizing because of the heat. Something in the throttle linkage is probably a bit tight, so any heat causes it to seize. It might even be the shafts that the throttle plates are mounted on in the carbs.

The fact that the water stream is very hot indicates that the engine is overheating. The problem could be the water pump, a restriction somewhere in the cooling system, a burnt gasket, or even a crack in the block or the exhaust plate.

I think you have to start by removing the gearcase and inspecting the water pump. While you have the gearcase off, connect a water hose to the water tube and turn on the water. Feel the surface of the engine and note if there are any spots that don't seem to be cooling. See if there is any water getting into the cylinders. You can start the engine with the hose connected like this and see if the engine cools. Don't rev too high when you do this. If the engine does not cool properly, you have a problem somewhere in the cooling system. See if you can determine where the the hottest spot is, or if the whole engine is heating up uniformly. Feel the exhaust cover plate on the starboard side of the block. If this gets hot immediately, the problem could be one of the gaskets in this assembly, or the gasket at the base of the powerhead. If this area stays cool, but the water jacket cover on the rear of the engine gets hot, the water jacket under this cover may be clogged.

"
 
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