1989 Johnson 25 HP Fuel Pump Test

[Jlockler]

Is there a way to test a fuel pump. I cant seem to find anything online, just rebuild videos but nothing that says what to look for to verify a pump needs to be replaced or rebuilt.

I have good spark on the plugs and compression is 90/90. If I can get the motor started it only runs for about 10 seconds before sputtering out, and its not often I can get it to turn over. Carb has been cleaned. Bowl float sits at 1 1/4". S/S needle is probably backed out about 1 full turn.

Primer solenoid works just fine. Key pushed in will force fuel into carb, however when I push the key in to prime the carb. The primer bulb on the full line isn't hard anymore. One squeeze will usually get it back hard. Is this normal? Does this mean thr fuel pump isn't doing its job?

 

[racerone]

The bulb is a manual fuel pump.-----If pumping the bulb keeps the motor running then that points to a defective fuel pump.-----The bulb absolutely does not need to stay hard when motor starts running !!-----A new $6.00 diaphragm will likely fix a defective pump.-----They are elegantly simple to inspect and repair.

 

[Jlockler]

If I push the ignition key in to activate the primer solenoid that will keep the motor running. Is that the same concept as manually pumping the primer bulb?

 

[racerone]

The primer solenoid is an electric valve.------Pushing the key in opens it.-----Fuel comes directly from the motor fuel pump and is put into the motor.----This fuel bypasses the carburetor metering circuits.----This would suggest that the carburetor needs attention.----The electric primer is a valve and it is NOT a pump.-----Pushing the key in is NOT THE SAME as pumping the bulb.----Understanding how things work will help you figure thing out.---Hope this helps you.

 

[flyingscott]

You also need to re check your compression with a different gauge. If the motor runs with the key in more than likely the fuel pump is good. The slow speed needle on them are usually at 1.5 turns out to start and will probably be closer to 2.

 

[Jlockler]

Why do you suggest checking compression with a different gauge? Are you suggesting the first compression test could be innacurate? I can rent one from O'Reillys and check with both.

Ill try manually pumping the primer bulb tomorrow as well as adjusting the slow speed needle to see if i can either rule out the carb or fuel pump.

 

[flyingscott]

because your compression #s are not good.

 

[Jlockler]

Lol the compression is 90 and 90 how is that not good

 

[racerone]

This is part of a " never ending debate " on what is good compression on an outboard motor !!!----Just like asking about oil mix ratios.-----Every one has their opinion.

 

[oldboat1]

My mid-'80s 9.9s have compression in the low to mid 120s. I think the question with your motor is how low is too low. IMO, it will probably run with 90 compression, if that is accurate, but it will be important to make sure that the ignition is spot on. If it's a matter of rings sticking, just running normally may show improvement. I would not increase oil ratios. Make sure the carb is squeaky clean in every orifice, and the air mix is properly set.

 

[Jlockler]

Thanks ill keep that in mind, motor has been running great here lately. The linkage was all off, once I reset it everything has been running pretty well. Starts up first try every time, idles and runs pretty well. Thanks for the input and help fellas