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Fuel Pump On 1985 75Hp Mariner

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I bought a newer boat & has a 1985 75HP Mariner on it. For some reason it won't run for long. I can pump up the bulb & it with start up & idle, but not run long in gear. If I pump the bulb the engine will run strong & fast for 20sec (rough guess) & then bog down & cut off. It did one day on glassy water got it to run for a long time, but if I went full throttle it would bg down & cut off. Or if I let up on the gas & then got back on it it would bog down & cut off. I thought it might be the carbs clogged. I took both carbs off & the top carb was a little dirty. I cleaned them & put them back on. Still having issues. I replaced the bulb (still same issues). I took the cover off to the fuel filter on the engine & had some gunk. Cleaned out & ran again & still having issues. Rechecked to see if any new gunk that pushed into it, & it is clean. When I do pump the bulb a lot the bottom carb will leak gas out but not the top. Checked the vent on gas tank & it is ok. Even tried with a different tank. Some times when you squeeze the bulbs it deflats & takes a little bit to become full again. A friend told me about a trick about priming gas line then putting your thumb over the line & run engine & see if it builts any pressure. I tried that & no pressure. My guess is the fuel pump isn't sucking the gas up & the carbs are running what gas is primed into them. I know some automotive things but new to outboard things. Is it easy or hard to replace the fuel pump. My guess is it is behind the black diagram behind the fuel filter that is held on by 3 bolts. Any help on this would be great.

Thank you this site is the best.

Chris

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I had the same problem on my 89 175 Mariner and thought that I would have to replace the fuel pump but my machanic just rebuilt mine for $100, ofcourse the majority of that was labor. I'm no machanic and was tickled to death with that. It sounds like you could do it yourself with a $15 - $20 rebuild kit. Good luck.

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If you haven't changed the fuel lines and bulb, do it. From the tank to the motor. The Ethanol in the gas can delaminate the inside of the fuel lines in a couple of years. The outside might look fine, but the inside is rotting.

When the hose pulls a vacuum, the inner hose lining seals off the inside of the hose. Make sure you use good quality fuel hose. The check valves in the bulb can go bad too. Do not buy a Wally World part. Get the OEM or equivalent.

Rebuild the fuel pump. It is very easy if you are somewhat mechanically inclined, under 1 hour.

If that doesn't solve your problem, inspect the inside of the gas tank. There might be something floating in there blocking the pick up tube.

You might want to think about doing a proper carb rebuild too. You do not want to run with a lean cylinder.

I hope some of this helps.

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I had the same problem on my 89 175 Mariner and thought that I would have to replace the fuel pump but my machanic just rebuilt mine for $100, ofcourse the majority of that was labor. I'm no machanic and was tickled to death with that. It sounds like you could do it yourself with a $15 - $20 rebuild kit. Good luck.

Those fuel pumps are a cinch to rebuild. I would also check your fuel lines to the motor and then to each carb. It sounds like you might be sucking some air.

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I am still having trouble. I replaced gas line & bulb to motor & checked the intake in the tank. no blockage or gunk. has anyone had issues with the gas lines in the motor area. I havent replaced any of the lines in motor area.

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As mentioned, the fuel pumps are fairly easy to rebuild.

Another item a lot of people don't know about, or think about, that can cause your problem is the anti-drainback valve in the tank. The barbed fitting in the tank the fuel line is connected to, if someone hasn't already replaced it, has a check ball in it that can be sticking. This is in the line to keep fuel from draining back into the tank from the fuel line. A coast guard requirement so if you have an engine fire, it can't be pulled into the tank by the fuel draining back.

Take the hose off the primer bulb that's coming from the fuel tank and see if you can blow back through it, into the tank. If you can, it doesn't have the check ball and don't need to go any further. If you can't blow through it, screw the barbed fitting out and replace it. I replace them with a straight barbed fitting and do away with the check ball.

One other check you can do is, with the engine cover off, pump the primer buld until firm and keep pressure on it while you closely check all the fuel line. If there is a leak anywhere in the system, letting gas come out, then it's probably sucking air there.

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if you have fuel leaking out of one of the carbs then you need to fix that, it is flooding over and will definitely cause problems at low speed. you need to make sure that the floats are shutting off before they bottom out. if gas is leaking from the bottom of the motor you can test the fuel pumpfor leaks. take the screw that hold it on out and squeeze the primer. if fuel comes out of the small hole in the back(where it attaches to the block) then you need to rebuild the pump. after that is fixed then try running it and keep sqerezing the bulb(becoming the fuel pump yourself) and see if it dies.

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Is it four cylinder if so I had same issue with my 125 it idles on two and runs on four my check valves were stuck flooding it down.they feed gas directly into the side of the cylinders if those lines are cracked it mite be another issue.

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