1988 70 hp Mercury 2stroke 3 Cyl is it the Fuel Pump

[bwhalerman]

This is what I've done.

1. Rebuilt and synchronized all three carburetors
2. New 3/8 fuel lines
3. New Primer Bulb
4. New spark plugs and wires
5. New water separation filter
6. Installed new thermostat and poppet valve

On sea trial yesterday the motor started without a problem. Idled without a problem. Ran at 3k and after a minute of two it bogged down. Squeezed primer bulb and motor responded. Decided to run a test.

1. 2k RPM for 3 minutes no problem
2. 2.5k RPM for 3 minutes no problem
3. 3K RPM for 3 minutes and motor bogged down slightly before 3 minute mark. Had to re-prime the motor to start it.

Took it out again today. Same result as noted. This time the female connector would not reconnect to the engine side fuel connector as the plastic sheathing around the pin that pushes against the ball in the female end was damaged. Went to West Marine and bought a 2 sided barb connector. Now the motor side of the water separation filter and fuel pump is one uninterrupted line. Took the boat out again and this time the same result as above.

New fuel in both tanks. No water in separation filter. When returning to the dock the motor stopped and was extremely difficult to restart. Had to prime the motor numerous times and finally got it started. No signs of leaking fuel anywhere.

I was thinking pull the fuel pump and rebuild again, make sure it is thoroughly cleaned and reinstall and try again. ANY COMMENTS OR SUGGESTIONS WOULD BE APPRECIATED.

 

[Texasmark]

I didn't see where you listed that you rebuilt the fuel pump the first time. The fact that you had to do the fuel pump's pumping action pretty much nails it as the smoking gun.
1. Need to get the right kit.
2. Need to pay close attention to the installation of the check valves and their component parts usually clearly defined in the accompanying instructions.

 

[James R]

I dont rebuild fuel pumps anymore. Sometimes they work sometimes they dont. I fit new.

 

[bwhalerman]

I didn't see where you listed that you rebuilt the fuel pump the first time. The fact that you had to do the fuel pump's pumping action pretty much nails it as the smoking gun.
1. Need to get the right kit.
2. Need to pay close attention to the installation of the check valves and their component parts usually clearly defined in the accompanying instructions.

Last night I pulled the fuel pump and it is what I expected and you knew. Before I opened it I blew air in both sides of the pump and it came out the opposing port. That told me it was probably the check valve. I finally got one right- When I opened the pump I saw that one of the check valves was no longer pinned to the body of the pump. Clearly the reason for the issue I posted was the fuel pump. I ordered an OEM kit that should arrive today. Looks like I can finally get back on the water this week.

 

[bwhalerman]

I dont rebuild fuel pumps anymore. Sometimes they work sometimes they dont. I fit new.

At $15 for a kit when compared to $125 it's well worth the effort. It's not a very complicated device and if a mistake is made a do over isn't too onerous. A simple trick I learned before installing is to blow into the in and out ports to make sure air doesn't travel out the other end. If it does there is a problem with the check valve.

 

[GA_Boater]

I dont rebuild fuel pumps anymore. Sometimes they work sometimes they dont. I fit new.

Why buy extra metal when the kit is a diaphragm and two gaskets, also 2 check valves if needed. Hard to mess up a rebuild. Especially when the pump is NLA and all that can be found is used.

 

[dpmsgeek]

I think your 88 is the same fuel pump as my 86. Only think is if it is still original it will need the two holes drilled larger for the check valves. Just follow the included directions and you will be fine.