1980 40hp Mercury o.b. motor Fuel problems

[Kdwellssr]

I have a 1980 40hp Merc o.b. motor. starts up good and quickly runs out of gas. I can see the fuel when it first starts in the sediment bowl. I've replaced everything including fuel pump rebuild. new fuel lines.. different tank, different fuel line ends. even bypassed the sediment bowl. Always with same results. Pump up pressure. engine starts up. Runs a minute or so as it is running the fuel out of the sediment bowl... then dies. I can keep it running longer if I pump on the inline rubber primer bulb when the fuel in the sediment bowl starts getting low. I am thinking about putting a electric fuel pump in line. Can it use a 3 to 6 lb fuel pressure pump. Has anyone ever done it? Will it work?

 

[Mercurylips]

Just sounds like your onboard fuel pump needs to be rebuilt.

 

[Kdwellssr]

That's what I thought as well I have done that. Only has a few gaskets.... Hasn't made any difference.

 

[racerone]

The fuel pump operates with a + pressure pulse from the crankcase and a slight negative pulse.-----Look for problems there perhaps.----I believe it should be easy to find the problem with the fuel system.

 

[Kdwellssr]

Looking for problems in the pulse of the fuel pump. If I unplug the fuel line and crank the engine it will shoot fuel four or five feet out of the 1/4" hose. Other than that I don't know what to look for?

 

[racerone]

Then there is nothing wrong with the pump !-----Is there a filter ?----Serial # of your motor ?

 

[Kdwellssr]

only filter is the sediment bow system. don't have serial number right now. it is a 1980 two cylinder 2 cycle, 40hp mercury.

 

[racerone]

If you have a cheap plastic tank then try another tank and hose !

 

[444]

So you did a fuel pump kit that came with the diaphragm and the check valve or just the diaphragm?

When you changed fuel lines did you put clamps on all connections so you don't suck air? I use gear clamps or EFI clamps, not zip ties or slip fit.

I would replace the sediment filter and the filter cup o-ring. There's a good chance you're getting an air leak somewhere because if there was a restriction downstream you might see your primer bulb get sucked shut, however for good measure you could run a line from your fuel pump to a jerry can and test it running on the muffs. A quick check on crowley marine shows a 1980 40hp with some kind of check valve before the fuel sediment filter assembly. If yours has it I would be checking that as well for blockage or air leak.

 

[Kdwellssr]

When I bought the motor it had no sediment filter in the bowl.. and the O ring was missing...so I replace them with new a few months ago.s number is 5898093. the only check valves I find are the two inside the pump. fuel goes from tank into the sediment bowl then out to the pump...from there to carb. I took it to have it tested and they say it has good fuel pump pressure. He said he had it running for about half hour. Got it home and same thing. Don't know if he lied or what. If I pressure up the fuel line it will remain pressured... No leaks.

 

[Kdwellssr]

Today I put a inline fuel pump on it to see what would happen. Started right up but soon became too much pressure and fuel came out of the little hole in side of carb that has a "jet" screwed into it. I took the fuel pump back off and it started right up.. and ran for about 10 minutes until I shut it off. Still has those fuel lines crossed making the sediment bulb after the pump.

 

[Kdwellssr]

Still thinking it's in the pump somehow.. as now the sediment bowl is after the pump and it still doesn't stay full.

 

[Kdwellssr]

What can be wrong with the pump system? Today I've bypassed the pump and installed a low pressure electric in line pump. Engine started right up. No excessive restarts or excessive choking. Sat there and ran good. Fuel sediment is still after pump and it stayed half full. Ran for 10 minutes just fine. Must be in the pump system somewhere somehow???????

 

[Kdwellssr]

I took it to the lake again and wouldn't ya know it wouldn't even start. I took it to the Marina shop and they won't work on anything older than a 87. So I took it home. That was last friday. Started messing with it again Saturday...figured why not can't get it to anybody that will work on it til Monday anyway. Finally decided to take the carb off a old motor I have and put it on mine just in case something was wrong with the carb.... Guess what. I found the problem. The mechanic that rebuilt the carb left a piece of old gasket on the carb. When he installed the new gasket it created a air leak. Took it to the lake yesterday and it ran fair... doing the minor adjustments. Today Took it back to the lake and it ran on the factory fuel pump without any help from the electric fuel pump I had to install. Finished the fine tuning and all is good again. Thanks to everybody that helped. Oh yeah one more thing. When the mechanic rerouted my fuel lines he had one line that was bent a little to tight... was actually kinking and shutting off fuel flow. I installed a new pieced of fuel line in that area with a nice loose loop instead of a sharp bend. Thanks again