96 50HP Johnson Pulse Driven Fuel Pump Fuel Starvation

[NautyBuoy]

Our 1996 50 HP Johnson carbuerated outboard originally had a VRO type pump. The oil pump was disconnected when I got it. Been using mixed fuel ever since.

Idles OK, runs fine in neutral at high speed but when actually in gear and under way, engine will bog down at anything more than 3/4 throttle. If I squeeze the primer bulb engine will run fine again, temporarily... Diagnosed by multiple mechanics who all said the same thing... Replace the pump. We did. Problem remains. Here's what we've done so far..

New fuel. No improvement
Fuel additives to clean out gunk in carb. No improvement
New tank hoses and primer bulb. No improvement
New Fuel filter. No improvement
Check for vac leaks None found
Tried known good fuel tank. No improvement
New pump, filter and lines. Slight improvement

Again, sqeezing primer bulb helps. With the cover off we can use the filter as a sight glass and see the fuel dwindling when the engine is under load. It's obviously a fuel starvation problem. What's not so obvious is why..

I am new to pulse driven fuel pumps and can't seem to find the exact OEM service manual for this engine. There are three lines leading from the fuel manifold. Two go to each of the 2 carbs.

The third line goes to a round device (some sort of fuel pressure sensor maybe??) with a couple of wires and a knob on top of a red indicator dial. (The knob resembles a tire stem cap)

Does this device control the "pulse" to the fuel pump? Is it adjustable? Where can I get an OEM JOhnson manual specific to this engine? Preferably something other than Seloc or Clymer.

 

[spingley]

Re: 96 50HP Johnson Pulse Driven Fuel Pump Fuel Starvation

What type of fuel hose clamps are you using? I had a similar problem once and found one of the hose clamps was not sealing the hose properly because it was the type that looks like a little mineature radiator hose clamp, and it was causing the pump to suck some air along with the gas, I replaced the clamps with ones that fit better and problem went away and fuel filter stayed full of gas.

 

[NautyBuoy]

Re: 96 50HP Johnson Pulse Driven Fuel Pump Fuel Starvation

Checked all hoses multiple times. But thanks for the heads up. I see from the posts there are some similarities in the Johnson motor complaints and would still like to get an oem manual if anyone knows where to go.

 

[spingley]

Re: 96 50HP Johnson Pulse Driven Fuel Pump Fuel Starvation

Checked all hoses multiple times. But thanks for the heads up. I see from the posts there are some similarities in the Johnson motor complaints and would still like to get an oem manual if anyone knows where to go.

I went on Ebay and bought a CD version for about 5 or 6 bucks.

 

[ezeke]

Re: 96 50HP Johnson Pulse Driven Fuel Pump Fuel Starvation

Get the factory manual from the printer: http://www.outboardbooks.com/index.cfm?fuseaction=search.search

The device with the red handle is your primer solenoid, used to enrich the fuel mixture for a cold start.

It's highly unlikely that your problem is the fuel pump.

All fuel pumps on Johnson/Evinrude motors are pulse driven except for a few V8 motors.

 

[NautyBuoy]

Re: 96 50HP Johnson Pulse Driven Fuel Pump Fuel Starvation

Thanks Spingey and Ezeke!!

Since my last posting 3 other mechanics have told me I bought a bad pump...

I really don't believe it. I disassembled the original pump after mounting the new pump and all diaphragms, o-rings, etc. looked brand new.... Not the typical weathered and brittle look associated with alcohol issues..

I'll go for the CD and see what it might tell me...

Once I find a solution I'll post it on an appropriate thread here...

 

[NautyBuoy]

Re: 96 50HP Johnson Pulse Driven Fuel Pump Fuel Starvation

Thanks to all that contributed... It was the carb(s).. Niether looked worn or gummed up but abut after a good cleaning and resetting floats runs like new again..