1976 40 Hp Johnson: Fuel Pours Out of Carburetor

[WaterWorldBoating]

I have a 1976 Johnson 40-HP model number 40E76A on a 1968 13 Sport, The engine will start and run great, but after running only about five minutes will die out like it has lost its prime. Pumping the fuel line bulb will just force fuel to flow out of the air intake and another hole in the forward side of the carburetor. Turning the key and fuel just pumps out too.

A marine mechanic put a new carburetor kit in it but the engine still had the same problems.

Second visit to the mechanic and he thought the choke was flipping open when we hit a wave or turned so installed a spring that held the choke. The choke would only work by manually pulling it out with this.

A third visit is pending.

My father thinks the float is sticking however with the carb rebuilt I would have thought this would have solved it.

When this first happened last year. Engine died out. Dad pumped the ball quite a bit thinking there was air in line. I hit the key and BOOM! The engine cover flew 10-feet in the air, plastic air cover was on fire, and fuel that poured out of carburtor into splash well also on fire.

I'd rather not scrap this motor since it seems like a carburetor problem, however I'm not looking for a repeat of last year's Whaler BBQ on the river. I welcome your thoughts and ideas.

-Chris

[jimh]

Usually in a carburetor there is a fuel bowl, which holds several ounces of fuel. The fuel pump operates continually, always trying to keep the fuel bowl full. Typically there is a float valve that controls the flow of fuel into the bowl. The float valve is operated by gravity or buoyancy. If there is not enough fuel in the bowl, the float is pulled down by gravity and opens the fuel supply so the fuel pump can fill the bowl. When the bowl is almost full, the float become buoyant, and shuts off the fuel supply--the fuel pump keeps pumping but can't pump fuel into a closed line. In operation of the outboard engine in waves, it is possible for the float to become stuck in either position. A hard landing can make the float valve stick.

The first problem described--engine stalls after five or ten minutes--sounds like the float valve became stuck closed. The carburetor bowl would become empty of fuel if the supply valve is shut off. The engine would eventually run out of fuel. The time to a stall would depend on the rate of fuel usage happening.

The second problem described--fuel pours out of carburetor--sounds like the float valve became stuck open. The fuel pump would keep pumping fuel into the bowl, which would soon overflow.

I am not familiar with this particular model Evinrude, but I don't think it has a choke circuit which works only on air. I suspect the device you call a choke is not an air restrictor but instead is a fuel enrichment device. That is the real purpose of "a choke"--to enrich the fuel-air mixture toward more fuel.

If a mechanic modified the fuel enrichment circuit, it could also lead to too much fuel, particularly if it was always operating. Engines usually to run well when there is too much fuel in the fuel-air mixture.

[Oldslowandugly]

As Jim said, it's probably the float/needle/seat assembly. Was the entire needle/seat changed? Sometimes "rebuilders" skip that. A brand new one should work fine as long as there is not debris getting in and jamming it open. Do you have a filter on the fuel line? I use a glass in-line filter right before the hand squeeze primer pump. According to the book you have an electric choke so it's simple to disconnect it for a test. It probably has a manual over-ride feature also. That would be a manual linkage on the side for you to actuate the choke should the electric solenoid fail. So check that too. It is unlikely that the low pressure fuel pump would overcome the float and flood the carb. I would concentrate on the float/needle/seat.

[jimh]

I had a 1976 Mercury 500 (50-HP) carburetor engine. The float valves would stick in the closed position if the boat landed hard in waves. After the engine stalled several times while rather too far offshore to row back, I learned that a rap on the carburetor bowls with the wooden handle of a screwdriver would jar the float valves to be unstuck. I had the carburetors serviced, but it took the mechanic two tries before the problem was cured. Apparently the seating area of the needle valve had accumulated some sticky stuff. Also, really old floats may no longer provide their original buoyancy, leading to a tendency for the bowl to overfill. If you are running at full throttle the fuel is used up rapidly, but if running at idle speed, it can soon overflow.

Also, it is common with carburetors on outboards that when the engine is tilted up to be almost horizontal some fuel is going to spill from the carburetors.

[Fisher18]

Was the needle and seat replaced with the kits?

Was the float replaced? If so, the float height adjustment is critical.

Ethanol in today's fuels plays havoc with old fuel system components.

[Oldslowandugly]

As Jim stated, I have found with carburetors that, when tilted, fuel drips out. So at the end of the trip I always run the carbs dry. Even with doing that I notice some drips in my splash well. That means when I next start the motor I need to prime with the squeeze bulb. This gives me an opportunity to verify that the floats are working and the needles are seating. My feeling is that leaving fuel in the bowls causes gumming which can make the needle stick open or closed.

[flymo]

As Jim stated, I have found with carburetors that, when tilted, fuel drips out. So at the end of the trip I always run the carbs dry. Even with doing that I notice some drips in my splash well. That means when I next start the motor I need to prime with the squeeze bulb. This gives me an opportunity to verify that the floats are working and the needles are seating. My feeling is that leaving fuel in the bowls causes gumming which can make the needle stick open or closed.

OLD'--I was always taught to avoid running dry multi-carburetor two-strokes. The rationale is that the carburetors don't run out of fuel mix at the same time, so one or more cylinders is running dry while the motor is still being spun by the remaining one(s). I never tried it so I don't know if it will be a problem for you. Apparently it has not done any harm so far.

I do know that, even with ethanol, it will take a long, long time for your carburetor bowls to gum up. Tilting the motor and getting fuel-drool is much more likely to be a problem for most users.

Flymo

[Oldslowandugly]

Flymo, yes, I've heard that rational before. I've been doing it this way since 1978 and I get many , many, years out of my outboard motors. I felt the fuel drool ( love that!) was dangerous. My feeling is that if a carb runs dry while the others are still running- there is no fuel left to wash the oil off the crankshaft needle bearings nor the cylinder walls.

[jimh]

On my six-carburetor Evinrude V6 225-HP engine, my strategy was to keep the carburetor bowls full of fuel when the engine was in storage. Because of good ground clearance on my trailer, I was able to keep the engine tilted down in an operating position when the boat was on the trailer and in storage. I would pump the primer bulb to fill all the carburetor bowls. When the engine was next started, it would be easy to get started, usually firing on a few rotations of the flywheel. So rather than keep the carburetor bowls dry, I tried to keep them full of fuel. I tried to avoid as much as possible ever tilting up the engine so the carburetors would spill out fuel.