1965 mercury 650 not sucking fuel

[74glasspar65merc]

I have a 1965 mercury 650 4cyl outboard that will not suck fuel. i thought maybe the pumps were bad but i cracked them open and everything is clean and in tact. can anybody help me diagnose this problem. i thought maybe the pumps were vacuum driven but now i dont think thats the case as i cannot find a vacuum line going into the block. the bottom pump has three lines. a fuel in, a fuel out to the carb, and a fuel line that runs to the pump right above it. the top pump has two lines. one to the carb and one to the pump below it. i have no idea how these pumps are driven but it would be easier for me to diagnose this problem. thanks for any help.

 

[oldman570]

Re: 1965 mercury 650 not sucking fuel

Replace the fuel line from the pumps to the carbs with a long hose to a safe distance from the motor, and spin the motor over while watching for fuel to come out of the hose. You should fill a quart jar fairly fast. If getting fuel there clean the carbs and replace all the fuel lines on them as ethnoial will eat the older rubber lines up and can cause the carbs to plug up. If not enough fuel in the jar check all filters, hoses, tank conections, and primer bulb for air leaks or blockage. Also make sure that the tank is vented good.
Oldman570

 

[CharlieB]

Re: 1965 mercury 650 not sucking fuel

The fuel pump is operated by the pressure and vacuum pulses of the crankcase. Either the pump bolts directly to the crankcase or there is a larger hose between the pump and crankcase. When this hose gets old, it 'flexes' and fails to conduct the pressure/vacuum pulses completely, and the fuel pump will not function to full capacity.

Another common problem is air sucking into the system, the pump doesn't seem to pump fuel. Simple test, replace a section of fuel hose between the pump and carbs, crank or start the motor and watch for any air bubbles passing thru the clear hose, showing air sucking in somewhere before the pump.

Remember to remove the clear hose once finished with your repairs, as clear hose is NOT rated, nor approved for fuel use except for very short time testing.

 

[74glasspar65merc]

Re: 1965 mercury 650 not sucking fuel

I replaced the "fuel in" line with a clear line and disconnected the "out to carbs" line from the carbs and I'm not even getting fuel through the clear line. Any other suggestions?

 

[oldman570]

Re: 1965 mercury 650 not sucking fuel

If your not getting fuel to the pump and caebs by pumping thr primer bulb, your problem is from there back to the tank. Try another portable tank and the old hose and see if you get gas. Brrow a portable tank and hose from a friend if you don't have one and go though prosess of elimination to find just what is causing the problem. Could be the primer bulb, hose fitting, tank pickup, or detereated gas line. Make sure that the primer bulb is in the hose in the correct direction and above the tank. Check the tank vent and any fuel filters for blockage. When replacing fuel hose use only new hose made for ethenoal gas as enthenoal will eat up old style rubber gas hose.
Oldman570

 

[CharlieB]

Re: 1965 mercury 650 not sucking fuel

We have been assuming you have good compression.

PROVE IT, as weak compression, a poor ring seal in the lower half of the cyl will not create the pressure and vacuum in the crankcase.

Test compression on all cyls.

Will it flow fuel when you squeeze the primer bulb?

Will the motor start, and run out of gas, die, unless you keep squeezing the primer?