Mechanical Fuel Pump

[weephee]

When I purchased my boat the motor came with a mechanical pump (original) and an electric pump. Both were connected in line. Talked to Don about it and he told me there should never be both a mechanical and an electric pump at the same time. Problem I was having was the engine was fuel starved once it sat for 10 minutes and then I tried to restart. I removed the electric pump, replaced the fuel lines, installed a squeeze ball between the filter and the mechanical pump, replaced the 2 micron filter and about two weeks earlier had the carb rebuilt. In order to start the motor, I must mechanically prime the pump everytime if the engine has sat for more than say 5 minutes. Is this normal with a mechanical pump. Also, do most of you have an electric pump. Perhaps this is the way I should go. The electric pump that came with the boat is not a good quality one. Thanks
Larry

[Mo]

You shouldn't have to prime the pump each time. You either have leak within the pump itself or a leak in the line somewhere...I'm thinking in the line.

If I had to deal with your situation I'd replace everything from the pick-up tube in the tank to the carb. Ensure filters / separators have good seal, proper elements etc. Either go with an electronic fuel pump OR mechanical. The problem might be as far back as the pick-up tube.

Someone had a previous fuel delivery problem with that boat and the "fix" was an additional electronic pump which likely primed the mechanical and kept a suction on the line.

[Al Schober]

Both the mechanical and electrical pumps move fuel. The beauty of the mechanical pump is that when the engine stops, the pump stops. The electrical pump requires an additional oil pressure switch to shut it off if the engine quits.
Both pumps use a diaphragm and a pair of valves to move the fuel. The parts in the mechanical pump are bigger and beefier and (to me) seem more rugged. The curse of the mechanical pump is the inlet settling bowl and it's seal. No real fix for these when they leak. If there were a way to saw off the settling bowl and go to NPT inlet, I would have done it. Failing that, I now have an electric pump.
Neither electric nor mechanical should lose prime in 5 minutes - the problem isn't the pump. The problem has to be between the pump and the fuel in the tank. Leaky filter? Leaks in the lines? Bad pickup tube?
If the problem goes away with a full tank, I'd suspect a bad pickup tube.

Al

[Carl-T705]

permit me a couple of questions Please

Does your engine start and then stall out because it's fuel starved or does it simply not fire up at all? If the air leak was the pump or line I can't see it pulling fuel out of the carburetor and preventing it from starting at all.
If it had an electrical pump and you turned this pump on with the engine off it would pressurize the fuel supply and you would see a leak if it were external. Is the pump and carburetor mounted higher or lower than the bottom of your fuel tank? The tank pickup would have to be lower the the carb to siphon backward. I suspect the problem is in the carburetor. Does it smoke black smoke like it's flooded with fuel when it does start? Hello everyone! from the new guy.

[weephee]

Mechanical Fuel Pump

Thanks for the replies. The fuel tank is higher than the carburetor. I had the carb totally rebuilt and I've replaced the fuel lines from the racor filter to the carb. I had the pick up tube out of the tank in the spring and it looked fine. I didn't vacuum test or pressure test it but there was no visible sign of a hole. Once the engine starts it runs fine at cruising speed. At idle speed in gear it seems to be starving for fuel ie. runs like it might quit until I increase the revs a little. There is no evidence of gas leaking anywhere and the fuel lines and connectors are totally visible. Exhaust is white not black so I don't think it is running rich. I have another mechanical pump that I will put on this weekend and see if that makes a difference. If the diaphram was leaking then perhaps it would lose its prime. If not that then I will remove the pick-up tube with a lot of difficulty and check it out once more. Thanks again for your help guys
Larry

[hanleyclifford]

If the diaphragm is leaking you might see an increase in oil level on the stick. This is potentially dangerous. Check for level and smell.

[weephee]

Mechanical Fuel Pump

Yesterday I changed out the mechanical fuel pump with a spare I had. Not a lot of access to the rear upper bolt and it took me about 2 hours to do it. Hooked everything back up and engine started right away. In a previous post I had said that I replaced the accessory drive because of a loud knocking noise. Well, the engine ran smooth and quiet for about 3 to 4 minutes and then as it heated up a noticable ticking noise started. Shut the engine off and let it sit for about 15 minutes and tried starting it again. It eventually started but I had to choke it for awhile and then it sorta sputtered to life and then ran great. When I got home, I tore the old mechanical pump apart and the diaghram is not ripped or torn but was extremely dirty and rusty inside. Bottom line is it is still losing its prime. I also removed the pickup tube in the gas tank and brought it home. I blew in one end with my finger over the other and couldn't detect a leak but I will unsolder the copper tube and solder in another one. Also checked the rubber gas lines and I still don't see any leaking. Any further comments would be appreciated on the ticking noise and the priming issue. It seems every time I go to the boat, I bring home a piece of the A4 to replace or rebuild. Thanks
Larry

[Dave Neptune]

Rust

weephee, rust in the pump is probably and indicator to your problem. A bit of rust could hold open a check valve and let the fuel syphon back to the tank BUT you say the tank is higher so that could not be it. A good filter should stop the rust. The rust indicates that some water and some metal got together where they shouldn't in the3 fuel system.
You should decide on using one pump or the other, then keep the one you don't use as an emergency spare.

Dave Neptune

[weephee]

Mechanical Fuel Pump

One more problem solved. I was totally wrong in my assumption as to why the carb was starving for fuel. In fact it was flooding. Problem was the wire that supports the little valve or plunger that stops fuel from entering the carb once the float is up was preventing the valve from fully seating. Fuel was very slowly still coming in and eventually leaking out the bottom of the flame arrestor housing. Over a period of 4 hours there was approx a full cup of fuel in the bilge. I took the carb apart for the 4th time and removed the wire hanger and put it back together and no more leaking and engine starts right up even after several hours. That means two problems solved this spring ie. the knocking noise and now the flooding carb. Just one more perceived problem with engine cooling system which I will start a new post on. Thanks again everyone for your help. Very much appreciated.
Larry

[ndutton]

Two thoughts Larry,

The issue remains as to where the rust came from in the first place. There should be none and unless resolved you risk a repeat (non)performance.

At the sailboat plants, we were often reminded that a single cup of gasoline in the bilge, once vaporized, had a potential explosive force of 3 sticks of dynamite. Please be very careful.

[Carl-T705]

weephee, it's an euphoric feeling solving mechanical problems!!! But Please be mindful of gas in the bilge. Consider placing absorbant material under carbs and fuel pumps when working with problems in these areas. The lower the octane the easier to go boom.

[weephee]

Mechanical Fuel Pump

Thanks for the warning. I was very nervous about removing the fuel. I opened everything up I could and then took paper towels and soaked up the gas. Fumes were really bad but it turned out OK. Hopefully no more spilled fuel.
Larry