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Jeff G.
Jeff G., Marine Mechanic
Category: Boat
Satisfied Customers: 4402
Experience:  39 years experience, Certified Master Technician, All Major Outboards, Sterndrives, Hi-Performance
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1975 evinrude 115 hp compression 106 to 115 starts and idles

Customer Question

1975 evinrude 115 hp compression 106 to 115 starts and idles perfect but want open up carbs have been rebuilt squeeze primor bulb while going it will open up and screem could it be vacum problem or what new fuel lines and pump
Submitted: 2 years ago.
Category: Boat
Expert:  Jeff G. replied 2 years ago.
Welcome,this question may need more than a single answer. Please post back with additional questions on this at any time.

You have either a bad pump, air getting into the lines, or a restriction.
If you have a built in fuel tank, check or remove the anti-siphon valve. This is a ball valve in the hose barb where the fuel line attaches to the tank. Remove the fitting and replace it with a full flow hose barb from any auto parts store.
Make sure all connections are snug.
Was the fuel pump rebuilt or replaced?
Customer: replied 2 years ago.
new fuel pump i have 1975 85 hp evinrude that runs perfect on this boat i put new plugs in changed coils changed power pack changed line and filter from tank to carbs what sends fuel into motor vacum or what
Customer: replied 2 years ago.
Relist: Inaccurate answer.
the problem is on the motor not the boat i have other motor that runs great on this boat
Expert:  Tan replied 2 years ago.

Hi my name isXXXXX will assist you.

.

The fuel pump on the motor is pulse driven by the stroke of the piston. Which makes the fuel pump pull fuel from the fuel tank and push fuel to the carbs. If you can squeeze the fuel primer bulb and the engine runs better you have an air leak from a loose fitting, a restriction in the boat side fuel system, clogged fuel tank vent or a bad fuel pump. To check for boat side fuel issue run the engine on another fuel tank. If engine runs better then you have a restriction in the boat side fuel system. If no change the fuel pump is failing and will need replacement. These are the only things that can cause your symptoms. Just because one engine runs on the boat doesn't mean the other will. This engine uses more fuel than the other creating more vacuum on the fuel system that the smaller engine. So just do these tests to eliminate all possibilities. Nothing is impossible.

Expert:  Jeff G. replied 2 years ago.
If you put a new pump on then get a fuel pressure gauge and put it between the fuel pump and the carbs, take a pressure reading. If the pressure is relatively steady then put the gauge in front of the pump and do a vacuum test for excessive restriction or air leaks. You can get a cheap fuel gauge at any auto parts store.
Jeff G., Marine Mechanic
Category: Boat
Satisfied Customers: 4402
Experience: 39 years experience, Certified Master Technician, All Major Outboards, Sterndrives, Hi-Performance
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