Outboard fuel pump problem.

[snowbird30ds]

I have a tohatsu 4hp stroke outboard and the fuel pump is being a PITA, it will work fine for so long then just stop pumping and the float bowl will not fill, it is only used with integral fuel tank which is higher than the carb so I'm thinking of just taking the valve flaps out and cutting a new carb to crankcase gasket without a hole for the crankcase pressure pulses so it is purely gravity feed only.
Any ideas why this would be a bad idea?
I've run the carb dry and pulled it over with the drain plug out and it does seem to be the pump part, the float is all clean and valve is good.
I've also 'borrowed' the valve flaps out of an old dead yamaha 8hp I have and it seems ok for now but every time I check it's ok for a while till I'm on a tidal run wanting to go the other way.

 

[VicS]

I have a tohatsu 4hp stroke outboard and the fuel pump is being a PITA, it will work fine for so long then just stop pumping and the float bowl will not fill, it is only used with integral fuel tank which is higher than the carb so I'm thinking of just taking the valve flaps out and cutting a new carb to crankcase gasket without a hole for the crankcase pressure pulses so it is purely gravity feed only.
Any ideas why this would be a bad idea?
I've run the carb dry and pulled it over with the drain plug out and it does seem to be the pump part, the float is all clean and valve is good.
I've also 'borrowed' the valve flaps out of an old dead yamaha 8hp I have and it seems ok for now but every time I check it's ok for a while till I'm on a tidal run wanting to go the other way.

The fuel pump on a 4 stroke surely is mechanically operated .... not by pressure pulses like a 2 stroke ?????

You do not say what year model it is so impossible to look up any details with confidence

I assume you have provision to attach an external tank ....... if so have you tried one ?

I am wondering if the external tank connector is not sealing and air is being sucked in through it?
Is the integral tank outlet valve opening properly ?
Is the fuel filter clean?
Is the pump diaphragm OK?

Why not try a connection directly from the fuel tap to the pump inlet to bypass all the external tank connection gubbins?

Or even directly to the carb so see if it will run by gravity feed? If it will then you can consider removing the pump altogether

Dont forget to include the filter in your final arrangement though

 

[snowbird30ds]

Oops forgot the 2 in 2 stroke, yes it is definately 2 stroke, no provision for portable tank the fuel pipe is direct from integral tank fuel tap to carb/pump, fuel tap is working fine, diaphrams appear to be fine.
Pump is integral to the float bowl, the model is M4C (3F9), there is no filter in the system as standard but may be one built into the tap.
I think I will just borrow a dinghy and try it on the local river before taking the motor back to my boat, if it will sustain flat out for more than a carbfull I recon it should be ok to use it gravity fed only.