1980 Mercruiser 260 - Mechanical Fuel pump has me baffled

**CanyonDoug** · 10-15-2017, 06:03 PM

Sight-glass had residue in it, and after wiping it out, running the boat for several more trips, it got more in. Fact manual (My vintage is 1979-1980 350) says to change fuel pump when you see fuel in the sight-glass (Now it runs through a tube to the carb I believe). SO, even though the engine was running, I decided to avoid having a breakdown due to a fuel pump failure. Ordered a new Sierra pump off Amazon. Hooked it up, but forgot to fill the fuel filter back up after having removed it.... maybe that was my down-fall? Anyway, engine did not get any fuel delivery, no matter how many cranks. Primed the carb with some fuel and it fired up right away and died momentarily after. Took the fitting off at the carb and put a rag there to catch any fuel. None. Blew air back through the line from duel filter to tank, just to make sure no obstruction and I could hear it bubble back into the tank. Hooked up again and still no delivery. Figured maybe I got a bad pump. Ordered another one... same issue. Was careful to make sure the arm was under the push-rod but still no delivery... even though I filled the filter back up with fuel.

No idea what to do now... Does the system need further priming somehow? Seems boats and even cars run out of fuel, which would suck the lines dry, and they start again when the tank is filled. But what are the odds I got two bad pumps? I would put the old one back on, but in all my curiosity to see the interior and spot where it might have been failing, it is in pieces or I would try it, just to trouble shoot pumps.

Help....! Thanks, Doug

**Dave Strong** · 10-16-2017, 11:09 AM

Remove the anti siphon valve at the outlet fitting on the fuel tank, take a long punch and knock the ball and spring out of the inside.

Dave

**CanyonDoug** · 10-16-2017, 12:44 PM

Originally Posted by Dave Strong

Remove the anti siphon valve at the outlet fitting on the fuel tank, take a long punch and knock the ball and spring out of the inside.

Dave

I will try that... but not sure if I can access it. Think that may be under the floor. Since I am the one with no experience, can you bring me up to speed on your hunch? Old pump worked fine, just started weeping.... ? I sincerely appreciate your input.

**Dave Strong** · 10-16-2017, 01:21 PM

You can blow air into the tank, thinking you can't draw fuel from the tank. Bad anti siphon valve would cause this.

Dave

**racervboat** · 10-16-2017, 02:45 PM

hook it up to a remote tank to the pump like an outboard with a primer bulb prime it run it and if it runs for a few minutes and don't run out of fuel its in the tank to the pump. Like dave said siphon valve stuck or dual filters sucking air of pick up tube broke off in tank.Easy to find out.

**CanyonDoug** · 10-16-2017, 07:45 PM

Originally Posted by racervboat

hook it up to a remote tank to the pump like an outboard with a primer bulb prime it run it and if it runs for a few minutes and don't run out of fuel its in the tank to the pump. Like dave said siphon valve stuck or dual filters sucking air of pick up tube broke off in tank.Easy to find out.

Thanks for the ideas, I'll see what i can come up with to hook up to the fuel pump. Metal line right now, maybe I can get a flare fitting from NAPA or somewhere to clamp some flexible line on to. Taking the tank and filter out of the circuit is a great start.. I appreciate th help. - Doug