1987 mercury 115 fuel problem please help!

[Thomas coe]

Today I rebuilt my fuel pump and replaced the fuel lines went to test out my work and the motor starts but after running for a minute the motor stalls out when I gave it gas. I checked the bulb and there's hardly any gas in it and I have to pump it up and get the motor started and same thing happens. I'm 90%sure I rebuilt it correctly. Need y'alls help. Thanks

 

[Texasmark]

If the bulb collapses when running you are looking in the wrong direction. The fuel pump is apparently sucking but sucking against a dead head somewhere. Squeeze bulb malfunction, hose degraded and particles clogging fuel line, fuel line strainer in tank clogged with varnish or debris, tank vent not venting.

 

[subliminaltrips]

sounds like a vent issue at the bulb or before as said above, do you have a way to check the fuel psi out of the pump? if its not the issue stated above thats where i would go next, but id almost bank on it.

 

[Thomas coe]

OK when you say tank vent I don't see one. Is it built into the cap like on atvs. Because on my tank there is only cap and the line to the motor. And could I check fuel pressure with a fuel line coming out of the fuel pump and into a bottle?

 

[Chris1956]

I would be looking for an air leak into the fuel line, between the primer bulb and the tank. If the fuel pump wasn't working, the primer would likely still be full of fuel.

 

[Thomas coe]

OK I will buy new bulb and line assembly and Crack open the fuel cap and see what we got

 

[Thomas coe]

OK test run was a failure will run once the system is primed but once the fuel is out of carbs just dies. Took outlet hose off of fuel pump and connected a hose going to a bottle and when cranking motor over it does not pump any gas. Does the motor need to be running for the pump to be operational. I'm at a loss.

 

[Texasmark]

Does the motor need to be running for the pump to be operational. I'm at a loss.

The primer bulb sucks fuel out of the tank and forces it through the fuel pump diaphragm and into the bowls of the carbs. When the carbs become full the float closes off the needle valves and flow to the carbs ceases. If the engine fuel lines are intact and the valves and diaphragm in the fuel pump are working correctly and not leaking, there is no place for the fuel to go and the bulb firms up and holds it......with moderate pressure from your hand.

Once the engine rotates, the sucking and blowing pressures from the crankcase act on the fuel pump diaphragm and check valves causing a sucking force on the inlet side....bringing in fuel from the tank, and a blowing force on the outlet side, forcing fuel down the line to the carbs. The flow capacity of the pump is adequate to force enough fuel down the line to adequately fuel the engine at WOT as the workings of the pump are directly related to how fast the cycles are applied to it which relate directly to rpm.........................

 

[Thomas coe]

Thanks for the reply. So if the pump is not pumping and I have piston psi. Then I probably have something wrong with the pump?

 

[Texasmark]

Thanks for the reply. So if the pump is not pumping and I have piston psi. Then I probably have something wrong with the pump?

Yepper, bad check valve or hole in diaphragm. Do you find any loose fuel around the bottom of the engine area inside the cowl? When you squeeze the bulb and get it firm, before starting, will it hold the pressure for 10-15 minutes? If yes and no, you may have some cracked lines letting bulb pressurized fuel out but on the input side of the fuel pump and the pump is ok but sucking air through the cracked line.

 

[Thomas coe]

All the lines are new and have fuel injector clamps on them. I think I might have bad valve. Took the pump off and made sure I had pressure for the pump and I do. Think I well just get another pump kit and check valve kit

 

[Texasmark]

Sounds like a plan