1989 30 hp fuel pump problems?

[cw00943]

I have a 30 HP yamaha outboard that would spit and sputter after running for about 30 seconds. If you would cut it off and crank it back up, it would run for another 30 seconds or so etc. I replaced the fuel pump diaphragm and then it ran perfect for a couple of trips to the water. And now the same problem has reoccured. From what I understand, whwn the diaphragm goes out, it allows too much fuel to cylinder 2 and fowls it out. What's going on here? Could it be a fuel pump?

[DeltaDawg]

I use a $15 Harbor Freight fuel pressure / vacume gage to check and see the fuel pump discharge is 3-6 psi while cranking at the discharge nozzel on the fuel pump, there is a test port nozzel in the middle of the fuel pump but it is more trouble to get that cap off then pull the hose that goes to the carb. The fuel pump keeps the carb bowl full until the needle valve shuts off the flow because the float pushed it up when the bowl filled. The behavior you describe sounds like fuel is getting used up in the bowl and not replenished which sounds like the float or needle valve is sticking the solution of which would be to clean and rebuild the carburetor. There is a good post by "rodbolt" on how he rebuilds carbs, he likes crc-06064 carb and choke cleaner, my local marine store carries that item.

It is not uncommon for the carb to get refouled by debris in the hoses and fuel pump diaphram so depending on the age and if you suspect you got bad fuel you may want to replace the hoses, filter and fuel pump diaphram connect the line to the carb last so you can purge the fuel path into a glass jar by pressing the primer bulb and look for water and debris in the fuel. Good luck.

P.S. 3-6 psi is a low reading to accurately measure you may have to zero calibrate that $15 Harbor Freight gage, there is a calibration screw on the dial, the bezel pops off. I hooked my Mighty Vac up to it and cycled it a couple times while adjusting the calibration screw, it turns hard and it kind of a course adjustment but got in on the nose after only a few tries.