Ready to Throw in the Towel on 1971 Mercury 500 50hp

Have been trying all summer to get the 500 50hp back to running condition. I thought we were close last week. Engine started right up, idled, ran well at full throttle, but had on going issue of having to pump bubble up to keep it running. Mechanic, replaced the floats, gasket and needle valve, and we took it out today to test it. Started up ok, warmed it up, went to full throttle, backed off on throttle a bit, died, we got it to start but couldn't get it to rev, and finally couldnt get it to start. Stuff done so far since we started this project, replaced spark plugs, solenoid, cleaned carbs, replaced floats, fuel filter, needle valves, all fuel lines, rebuilt fuel pump, replaced remote throttle control, throttle cable, shift cable, water jacket gasket, new fuel tank, new primer bubble, lines and connector for fuel tank to engine. He doesn't have any other ideas.......I'm not a mechanic so I don't either...it has ran well a couple times this summer but not reliably. Oh and he replaced all the wiring in the motor that was dry rotted or pack rat damaged. Any one have any ideas, it would be greatly appreciated....otherwise going to sell it a piece at a time on ebay LOL.

Re: Ready to Throw in the Towel on 1971 Mercury 500 50hp

You said initially that squeezing the bulb kept it running. Did you try the same thing again after the floats, gasket and needle valve were replaced? If you can keep it running by squeezing the bulb, it points to a problem with the fuel pump as when you are doing the squeezing, you have become the fuel pump.

Gerry

Re: Ready to Throw in the Towel on 1971 Mercury 500 50hp

Thanks Gerry, we tried to keep it running by squeezing the bulb, it would rev a little higher by itself (throttle full open) but wouldn't run much past a fast idle. Last week when it ran ok...I had to do what you were mentioning about being the human fuel pump.....this time it did work.

Did the ball ever get hard?

I have to also say you still have fuel delivery issue. And even though you replaced the fuel pump, that would be my first look see again. Make sure the pump is working properly because it sounds like the fuel diaphragm is either got a hole in it or something in that line of issues. Possibly the one way check valves are not working in the pump. Also check for possible cracked fuel lines if you haven't already checked and changed them. As for not revving up when there is fuel, check the timing advance system. Could be that is not tracking the throttle opening correctly. Don't give up yet. There is more suggestions on here from the experts I'm sure.

Guys - Skaggs hasn't been here since July. So this is an old one.

Jackson - If you have a problem, please start a new thread. Thanks.