1986 Johnson 50 fuel problem under load

Oldnbold

Seaman
Joined
Jun 27, 2017
Messages
60
J50tlcde. New to me
Problem: will not run on both cylinders when under full acceleration after approx 10 seconds. If I keep squeezing the bulb making bulb rock hard it’ll run indefinitely under hard WFO. Let 10 seconds (or less) go by w/o squeezing and it’ll drop a cylinder. Squeeze to hard and get cylinder back.
Compression: 120 psi both cylinders . When I got it, among other things, I cleaned the carbs and replaced all new fuel lines. Engine starts easily cold and idles well for a while then it’ll surge faster then slower
The oil side of vro was disconnected and uses premix now.
to me, it sounds like I need to replaced the diaphragm on the fuel side of the vro pump as I don’t know it’s history. I have not put a vacuum gauge on the suction hose for the fuel pump but I will soon.

does the problem sound like a faulty fuel pump diaphragm to the experts ?
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,415
Perhaps test run with a known to be good hose and tank.-----Actually the pumps work on a + PRESSURE pulse.-----There is a simple ( non mixing ) pump available that attaches to the side of the top cylinder.-----You remove the plug in the pulse port and the pump mounts with 2 screws ( 10-24NC ) and a gasket.-----Find the part # on an 84 model like yours or on the later 48 HP models.
 

Oldnbold

Seaman
Joined
Jun 27, 2017
Messages
60
I’ll look into adapting an ‘ 84 fuel pump. What do you plug the existing pulse port with?
 
Top