Still stumped on engine miss.

[bostonwhalermontauk1965]

Does anyone know what would constitute a fuel pump needing to be rebuilt on a 1982 Johnson 50? To me all it looks like is a diaphram type rubber plate behind a screen. So presumably if the rubber is not torn , it is fine? I am going nuts trying to find out why I have an upper dead cylinder even after rebuilding both carbs and both cylinders firing perfectly and both having 135 lbs of compression. Checked cylinders with a timing light, installed new ignition wires and plugs. At wits end and ready to give it to the pros.. Thanks in advance - Paul

 

[Daviet]

Re: Still stumped on engine miss.

Have you checked the fuel pump pressure? Does the fuel pump mount to the top cylinder? Maybe the pump is leaking internally and flooding the cylinder, if it mounts to the upper cylinder.

 

[eavega]

Re: Still stumped on engine miss.

Have you considered the fuel lines? A cracked or otherwise faulty fuel line or connector can bleed air into the system and cause a miss. For what it would cost to send to a mechanic, you could replace the fuel pump and all the lines from the tank to the carburetor. As for the simplicity of the pump, don't let it fool you. I had a faulty pump that didn't get fixed with a rebuild. The problem turned out to be the plastic piece of the pump had developed a crack, and when it warmed up it would expand and leak air into the system. A new pump fixed me right up.

Rgds

 

[bostonwhalermontauk1965]

Re: Still stumped on engine miss.

Thank you both for the advice. It may be a bad pump then. I replaced everything brand new from the fuel tank, lines, bulb and connectors. The entire fuel system is new from front to back excluding the pump. And yes, the pump does mount to the top cylinder, so maybe that is the issue. I will look into that. Thank you.

 

[bostonwhalermontauk1965]

Re: Still stumped on engine miss.

What is the best way to check fuel pump pressure, and how many psi should there be? The primer bulb dosent get that hard, and it did stall the motor when I pumped it while the motor was running.

 

[boobie]

Re: Still stumped on engine miss.

Take the pump off and put some nuts on the screws that hold the pump on and tighten them. Then pump the primer bulb and check for any fuel coming out of the pulse hole that goes to the cyl. If you get any fuel, the pump is bad causing the cyl not to run.

 

[bostonwhalermontauk1965]

Re: Still stumped on engine miss.

Boobie - Thank you very much for your post. It was another test to eliminate yet another aspect of my nightmare. I did perform the test you mentioned just now, however no fuel came out. I did order a rebuild kit for the pump from iboats and am waiting for it, however I guess we just proved that the pump is not fouling out the upper cylinder. The diaphram inside the pump is extremely stretched out. It was like inverted and I dont see how it could be pulling and pushing from an engine pulse. I guess I could try to hook up an inline pressure gauge or at least disconnect the hose while motor is idling and see what kind of flow I ge. I am really out of ideas and frustrated because I feel as though I have tried everything now. I was hoping your idea was going to show a leak because at least then I would have had an answer. Thank you anyway - Paul - any other thought on this?

 

[AlTn]

Re: Still stumped on engine miss.

you can "gravity feed" the carb from another fuel tank...I've used an old lawn mower tank a couple of feet above the carb...and watch the outflow of the fuel pump while at idle...just leave the hose on from the pump to carb and catch the flow in a container....you should have a steady pulse of fuel with no interruptions

 

[bostonwhalermontauk1965]

Re: Still stumped on engine miss.

This is another great idea. I will set something up to gravity feed motor, while still monitoring the factory fuel pump on the other side with the motor running. I really want to isolate the actual problem, rather than repair 5 unknowns at once and then wonder what was really wrong with this motor. Thank you all for all of your help. I can say that it is really amazing how awesome this motor behaves on one cylinder, and when it is running right on both, it will really be great because I went amazingly fast thinking the problem was corrected on half a motor. Thank you all again for all your input

 

[boobie]

Re: Still stumped on engine miss.

When you have the mtr running, have tried to squirt some premix in the cyl that is dead and see if it picks up?? When you say good spark, will it jump a 7/16" open air gap on a spark tester??

 

[bostonwhalermontauk1965]

Re: Still stumped on engine miss.

I have to try the squirt bottle trick - havent been able to do that yet because it has been raining here. And yes, when I say good spark, I have seen it jump to ground out of the coil pack, blue in color probably almost 3 inches away. I was amazed at the awesome spark it has. That is why I am so pissed off that I am leaning towards a fuel problem here even after rebuilding the cars (properly) without taking any shortcuts at all. Brand new fuel system from front to back including tank, 135lbs of compression in both cylinders, new wires and plugs, (multiple sets when I even second guessed possibly fouling the first 2 pair with all my testing. Your idea of testing the pump off the motor was an awesome one. It passed the non leaking out the back test. however, what move do I make next other than to squirt some gas into upper carb while running? I also like other idea of gravity supplying the carbs and watching performance of the factory pump with hose off while running - that is another great idea!! Thank you all soooo much. Sooner or later I will figure this out, It is going to end up being the last thing I try to test before I find culprit - going nuts on this one.... Ive put together motors brought to me in milk crates, but cant figure out a miss in a little outboard... LOL

 

[bostonwhalermontauk1965]

Re: Still stumped on engine miss.

Does anyone know where I can pick up a squirt bottle to accept gasoline that the gas wont eat away?