1976 evinrude 85 hphow does the fuel pump work?

[matt85evinrude]

hey boaters! anyone tell me how fuel pumps work on these engines? i just want to know out of curiosity. also how do you tell if its a bad pump!? thanks guys!

[levi_tsk]

behind the fuel pump theres a small hole and as the piston goes up and down it creates a push on the downstroke and a pullon the compression stroke on the hole also know as a pulse signal this pulse signal acts on a diaphram inside the pump and the pump has two one way valves in it and when the diaphram gets pulled it in turn pulls fuel into the pump and then gets pushed and pushes the fuel out of the pump towards the carb this happens many times a second and inturn creates your fuel pressure

theres a bunch of ways to test a pump the easiest way is to take the hoses off the pump and take a clean hose and put it on the outlet (carb side) of the pump and blow into the hose - it shouldnt blow if it does its badand you need to rebuild it (parts are about 10 bux us) but this isnt fool proof as sometimes it wont blow and itll still be bad

[matt85evinrude]

so you think replace mine if i thinks its faulty?

[levi_tsk]

no, do the checks i gave you first .....

[emdsapmgr]

I'd probably want to run the engine and see what develops before replacing the pump. While not expensive, it may not be necessary. A fuel pump should provide enough fuel to run the enigne strong at full throttle/rpm. A weak pump won't provide enough fuel to keep the engine going at high rpm. It may run strong, then fall back in rpm's (while the pump refills the carb bowls) then it may take off again. A process that repeats. The thing to keep in mind with this engine is that all the original fuel hoses were not equipped to handle USA fuels which have ethanol in them. If you have ethanol blended in your New Zealand fuel, it will deteriorate the rubber parts of the original factory fuel system, which will include the hoses as well as the rubber bladders inside the pump. Bits of fuel hose can actually lodge inside the carb jets, causing restrictions. Today's replacement parts are all ethanol resistant.

[eavega]

Note also that on these models, the pulse that drives the pump does not come from the hole in the back, rather it comes from one of the three hose connections (the one at the back of the pump, if memory serves). Also, tread lightly when deciding to re-build the fuel pump. The pump on that motor was not designed to be serviced (although rebuild kits are available), only replaced. Make sure you keep track how the pump is assembled, inside there are two small leaf valves, two plastic caps with springs, the diaphragm, and gaskets. Everything has to go back in the right order and in the correct configuration in order for the pump to work correctly, and that can be tricky (especially the caps, they need to be just right, or else the diaphragm is stretched out incorrectly and the pump won't pump). Additionally, since they were not meant to be rebuilt, the gaskets are pretty well adhered to the different plates on the pump, so you have to carefully work them off. The upshot is that if you do need to service the fuel pump, and you are successful in rebuilding rather than replacing, you can save yourself about $70. I had a previous thread about rebuilding the fuel pump on my 70 HP Johnson, and someone was kind enough to provide a diagram that roughly corresponds to your fuel pump. This along with pictures I took during disassembly were invaluable in correctly re-assembling my rebuilt fuel pump.

Good luck!

Rgds

[F_R]

Simplest way to "test" a fuel pump is to give the primer bulb a squeeze while the motor is running poorly. If it picks up and runs better for a few moments, suspect the fuel pump.

The "correct" way to test a fuel pump is to tee a pressure gauge in the line between the pump and carburetor. Read the pressure while running.