Fuel Pump Savvy

[chunkachange]

I have a 2003 Mercury 5 hp 2 cycle outboard that will start when choked, run for 5 seconds and die like it is out of gas. Is there a way to check to see if the fuel pump is working properly, and that the problem is NOT some other reason like clogged exhaust, leaking head gasket, etc.?? I do not want to pull the head and get into bigger problems if unnecessary. Thanks, Chunk

 

[eurolarva]

Re: Fuel Pump Savvy

I doubt that motor has a fuel pump. Isnt it still under warrenty? Maybe try a blast of carb cleaner into the throat of the carb.

 

[chunkachange]

Re: Fuel Pump Savvy

Yes, it has fuel pump attached to the carb...a rectangular plastic affair with various thin sections of neoprene and little wafer thin tabs sandwiched together with four screws. Chunk

 

[DHPMARINE]

Re: Fuel Pump Savvy

If you start the motor,and it only runs for 5 seconds,it's not the fuel pump.the carb has enough gas to run at least a minute.<br />DHP

 

[eurolarva]

Re: Fuel Pump Savvy

The primer will last for 5 seconds. The float to the carb may be stuck closed and there may not be gas in it

 

[chunkachange]

Re: Fuel Pump Savvy

After starting the motor by choking it, I can drain a full bowl of gas from the carb bowl. I checked the float and it moves freely, the pin and tiny spring holding it to the float are all in perfect condition. I sprayed carb cleaner in all parts of the carb, completely dissasembled, blew out with compressed air, reassembled, put new carb to motor gasket on....and it still runs when choked for 5 seconds and dies for apparent lack of fuel. Any more suggestions would be appreciated. Chunk

 

[chunkachange]

Re: Fuel Pump Savvy

I cleaned the carb again and took the fuel pump apart and inspected and all looks perfect. Put everything back together and blew air gently into the fuel inlet and heard a "chirp" sound from the carb, probably a valve opening. When I tried to suck air back out, I could not, so that must mean the check valves are ok. I wound the air screw all the way in and backed it out one and one half turns, like spec says to do. I have not put the carb back on the motor yet. If it still runs only when the choke is pulled out momentarily and shoved back in, and runs for only 5 seconds and dies, then what else could be the problem? Any ideas on what to check and I will check it. Thanks for responding, I am baffled! Chunk

 

[sonar4]

Re: Fuel Pump Savvy

I have experienced this confounding issue with my Merc too. What I found was a tiny port in the main jet gland (fuel passage from bowl to venturi) had become clogged from winter rest. This port is essential to the atmospheric operation of this carb! <br /> Remove the fuel bowl and main jet (only if it's in the very bottom of this passage). Look for a small port leading off at an angle, sometimes the casting will give an idea where it should be. Remember, this port is only a few thousanths of an inch. I ran a thin wire up there followed by carb spray followed by a healthy blast of air.<br /> If you block the vent hole in the carb mount base and shoot air into the carb front vent hole you should get air flying out the main jet passage. If not it's still plugged.<br /> I almost went to the rubber room on this one, but when I put it back on all worked grand!

 

[BillP]

Re: Fuel Pump Savvy

For future reference on the fuel pump. I've had the neoprene diaphragm look ok but be porous enough not to prime or keep the engine running. Usually you can see they are bad but not always.