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1972 Mercury 85 HP Outboard: Loses fuel pressure and dies

rasmus07

New member
I have a 1972 Mercury 85 HP OB that will start and get up and out initially. Then after about 3-4 minutes it slows down dramatically and dies. It starts up again and then acts like it loses fuel pressure and dies. I have a hunch it is the fuel pump but am not sure.

Any ideas?

Steve
NP NE
 
Fuel Line Routing.JPGBe sure the tank vent is open (leave the cap off as a test). If that doesn't do it, look for air leaks before the pump, and a fuel hose that is run as shown below.

Jeff

PS: I've been using reinforced clear hose for a year now that allows one to SEE the fuel inside the hose. That's how I discovered HOW the fuel line mus be run--it was half full of air all the time!
 
Jeff,
I will try that. I have a feeling the line may be crimped or that a constant fuel flow doesn't exist.

Thanks

Steve





View attachment 4888Be sure the tank vent is open (leave the cap off as a test). If that doesn't do it, look for air leaks before the pump, and a fuel hose that is run as shown below.

Jeff

PS: I've been using reinforced clear hose for a year now that allows one to SEE the fuel inside the hose. That's how I discovered HOW the fuel line mus be run--it was half full of air all the time!
 
If it still fights you, 'tee' in a fuel pressure gage after the pump and see what pressures are developed: It should pump up to 10 psi or so on the bulb, run 2 to 3 at idle, and make about 4 psi at full rpms.

Jeff
 
Jeff, The advice was perfect. I replaced the fuel line and then made sure the pressure cap screw was open and we had a blast in that little 1972 Mark Twain 15 ft tri-hull. Thanks! Next step re-wire my tail/stop lights on the trailer. Always fun in boat ownership.

Steve



View attachment 4888Be sure the tank vent is open (leave the cap off as a test). If that doesn't do it, look for air leaks before the pump, and a fuel hose that is run as shown below.

Jeff

PS: I've been using reinforced clear hose for a year now that allows one to SEE the fuel inside the hose. That's how I discovered HOW the fuel line mus be run--it was half full of air all the time!
 
Good deal.

Jeff

PS: Looking for an 85 hp power head for my winter project. If you come across one please let me know.
 
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