Motor starving for fuel unless I occasionally pump the primer bulb

[floatfan]

I did some maintenance on my little boat which hadn't seen the water in a couple of years. 1980/81 Merc 9.8. I cleaned the carbs and replaced the gaskets, as well as replacing the water pump impeller. Also replaced the fuel lines with the new blue hoses and installed a new primer bulb due to the old one being stiff. At the river Saturday, the boat motor was running like a top, but after a minute or so, depending on the throttle, would seemingly run out of fuel and die. I noticed that while running, the primer bulb didn't seem like it was full. I ended up driving with the tiller in one hand and the primer bulb in the other, and about every 15 seconds would pump it. No problems as long as I did this. What could cause the lack of draw in my fuel line?

 

[floatfan]

Re: Motor starving for fuel unless I occasionally pump the primer bulb

Googling has me believing that it might be the diaphragm, which didn't come with my carb gasket kit. I just reused the old one.

 

[Mi duckdown]

Re: Motor starving for fuel unless I occasionally pump the primer bulb

Rebuild the fuel pump and enricher/ choke. should be good to go.
You bought a kit that did not come with fuel pump rebuild.
I buy the gasket kit, that comes with everything fuel related. carb/pump,enrichter/ choke.
once you have pulled the carb, repalce everything.

 

[SilverSS07]

Re: Motor starving for fuel unless I occasionally pump the primer bulb

Possibly the fuel pump. Check the fuel lines going to the pump and to the carbs also.

 

[floatfan]

Re: Motor starving for fuel unless I occasionally pump the primer bulb

Rebuild the fuel pump and enricher/ choke. should be good to go.
You bought a kit that did not come with fuel pump rebuild.
I buy the gasket kit, that comes with everything fuel related. carb/pump,enrichter/ choke.
once you have pulled the carb, repalce everything.

Gasket kit had 5 or 6 gaskets, but not the diaphragm. Quite honestly I'm not sure where the fuel pump is on this motor. The fuel line connects to the motor, then has a 6 inch or so hose that runs to the carb.

 

[floatfan]

Re: Motor starving for fuel unless I occasionally pump the primer bulb

Possibly the fuel pump. Check the fuel lines going to the pump and to the carbs also.

Is this the fuel pump? (not my motor...but looks identical)

 

[Mi duckdown]

Re: Motor starving for fuel unless I occasionally pump the primer bulb

NO . were that fuel line (red arrow ) goes to the carb, that is your pump.
On side of the carb.

 

[floatfan]

Re: Motor starving for fuel unless I occasionally pump the primer bulb

In that case, it did come with those gaskets, which I replaced (I was calling the whole thing the carb). It didn't come with the diaphram inside there though (diaphram may be the wrong word...but it goes against a gasket and is a thin permeable material). I just reused the old one, though it didn't appear to be torn.

 

[Mi duckdown]

Re: Motor starving for fuel unless I occasionally pump the primer bulb

That is were you went wrong. It only takes a pin hole that you can't see or just worn out. Rebuild the pump. It will come with extra parts that you may or not need. replace with the parts you need.

 

[Chad N]

Re: Motor starving for fuel unless I occasionally pump the primer bulb

Anti-siphon valves on the fuel tank could also cause that issue. Does it have a portable tank or onboard? If portable try hooking it up to a different tank.

 

[floatfan]

Re: Motor starving for fuel unless I occasionally pump the primer bulb

That is were you went wrong. It only takes a pin hole that you can't see or just worn out. Rebuild the pump. It will come with extra parts that you may or not need. replace with the parts you need.

Will do. Thanks for the advice!

Anti-siphon valves on the fuel tank could also cause that issue. Does it have a portable tank or onboard? If portable try hooking it up to a different tank.

It's a 6 gallon portable, but I've had the tank for nearly 10 years. My air vent was open on it, and I've never had issues in the past with it. In fact, I even unhooked and unscrewed the fitting on the tank thinking maybe it was a blockage in there. Put the hose straight into the tank and same problem. Thanks for the info though.

 

[CharlieB]

Re: Motor starving for fuel unless I occasionally pump the primer bulb

Like duckdown said, the fuel pump IS that side of the carb, if the diaphragm is 'hardened' and no longer as flexible as required, it will not fully pulse and pump enough fuel for large throttle.

Another possibility is aftermarket quick disconnect fuel fittings found on fuel hose/primer bulb assys. The O-rings often fail to seal under vacuum and allow air to be sucked into the system, reducing fuel flow to the carb. The test for this is to temporarily install a clear hose between the motor fuel fitting and the carb, start and run the motor while watching this clear hose. Any air bubbles passing thru prove air is sucking into the system.

REMEMBER to replace the clear hose once finished with testing and repairs, the clear hose is NOT RATED and not approved for fuel use.

 

[Mi duckdown]

Re: Motor starving for fuel unless I occasionally pump the primer bulb

Good point CharlieB