Fuel leaking from exhaust on cold start

[donnie remesco]

can anyone tell me why my 1992 55hp yamaha c55elrq leaks raw fuel though the exhaust on start up, and what I need to fix the problem, .... also, the fuel intake seems to be faster than the priming ball can handle, so at full throttle the ball will empty, and needs to be pumped up again to continue operation, and are these two problems related?...Any help would be appreciated,... thanks

[99yam40]

when was the last time you replaced the fuel pump?

[Jason2tpa]

can anyone tell me why my 1992 55hp yamaha c55elrq leaks raw fuel though the exhaust on start up, and what I need to fix the problem, .... also, the fuel intake seems to be faster than the priming ball can handle, so at full throttle the ball will empty, and needs to be pumped up again to continue operation, and are these two problems related?...Any help would be appreciated,... thanks

In bold above...like 99yam mentioned, this symptom is related to fuel pump failure. And I recon if you're over-priming to keep engine running, this might explain the raw fuel out of exhaust.

99yam...isn't it possible to force fuel via primer bulb while engine is running, thereby keeping float needle valve open, and thus flooding the cylinders?

[99yam40]

nope. float will close off the needle and seat and stop fuel flow into bowl when it raises

[Jason2tpa]

nope. float will close off the needle and seat and stop fuel flow into bowl when it raises

Gotcha. Is there another way for raw fuel to exit the exhaust other than from the cylinders exhaust port?

[99yam40]

not that I know of, it has to go threw the cylinders to hit the exhaust

[donnie remesco]

two days ago,....it was the first thing I did,.... the situation didn't change.

[donnie remesco]

already changed the fuel pump,... and fuel still comes through, without prime.

[jham0077]

Float stuck, or full of fuel and not floating anymore?

[robert graham]

Is your Primestart lever in the "on" position?.... Should be in "automatic" position...

[99yam40]

I do not believe the last 2 comments would make it run out of fuel where you would need to pump the bulb to get fuel back into the carb bowl

[panasonic]

What kind of boat is this engine on? Tank is not higher then the engine by chance?

[donnie remesco]

yes, tank is higher,.... it's a pontoon.
the fuel stops coming out of the exhaust, within a couple of minutes of operation

[panasonic]

I figured as much..my hunch is the same as the others, bad fuel pump and/or a bad needle valve in the carb...I am leaning more towards the carb.If the needle and seat are not perfect and then you add gravity from the fuel tank being above the carb/engine....recipe for leaking fuel.

See it many times on motorcycle and snowmobiles. That is pretty much the reason why many motorcycles have fuel shut off valves on the fuel tank.

[boscoe99]

yes, tank is higher,.... it's a pontoon.
the fuel stops coming out of the exhaust, within a couple of minutes of operation

Float activated inlet valves can seem to be a bit funky at times. With just a little bit of pressure on the needle valve the valve may not seat completely and fail to stop the flow of gasoline. With a tad more pressure, or maybe a lot of pressure, on the float, the valve may close tighter and prevent the flow of any gasoline.

The faster the flow of fuel into the float bowl the quicker the pressure rises causing the valve to seat tighter. The pressure from just the elevated tank alone may be insufficient to cause the float to seat the valve. When the motor starts the fuel pressure quickly rises to a higher pressure, resulted in more fuel being supplied to the carburetor, causing the float to rise higher. The float trying to go higher causes the valve to close tighter.

Makes it seem strange that with more pressure the valve seals whereas with just a bit of pressure it may not. Counter to what conventional thinking might suggest.

This is sometimes seen in power trim and tilt assemblies. Stop the motor from going up by just deactivating the UP switch and it might bleed back down over time. Power it down for a nanosecond and the increased hydraulic pressure might result in a check valve seating that otherwise might not seat.