Fuel pump (?) on 77 Johnson 15

[Karl Northman]

I've got a 1977 Johnson 15 that was running fine last year - launched it this week and it runs okay at idle, and while it's cold, but when it warms up, if you open the throttle up the thing just goes rapidly to zero RPM - takes maybe 3 seconds to shut down, and then it doesn't want to run more than a few seconds after starting again.

Figured it had a fuel problem, rebuilt the whole fuel hose, no change. But then, while it was running, I tried disconnecting the fuel line entirely, because watching the temporary transparent hose it didn't seem to be sucking. Then I discovered that the engine, once you've used the primer to fill the carb, runs just fine as long as it doesn't have a fuel hose connected at all. (It runs much longer with no hose than it does with a hose).

I'm thinking that maybe I've got a hole in the fuel pump diaphragm that is sucking gas into the engine and screwing up the mixture. The way the engine dies is exactly the way it would die if you pulled out the choke while it was running and warm.

Any ideas? Is this plausible?

 

[bktheking]

Re: Fuel pump (?) on 77 Johnson 15

If you feel adventurous OMC sells a fuel pump rebuild kit with instructions for next to nothing to replace all the inards. Worth a shot, sounds like it may be the issue. The spark plug in the cylinder that runs the pump would look different than the other as a telltale sign.

 

[raczekp1]

Re: Fuel pump (?) on 77 Johnson 15

http://www.sschapterpsa.com/ramblings/Rebuilding_fuelpump.htm

 

[levi_tsk]

Re: Fuel pump (?) on 77 Johnson 15

did they still use this pump or is it a different one? get the BRP kit as it includes instructions pn #393088 if its the small square pump shown above
make sure you blow test it when youre done if you blow in the inlet it should blow and if you blow in the out let it should not blow these can be a bit of a pain so take your time and bring your patience