Carborateur and fuel pump removal

[ckohler0529]

Can anyone recommend a good step by Step reference for removing the fuel pump and the carburetor? Thanks.

[roadnsky]

The carb we can talk you thru easily. Couple of bolts and hoses.
I'll try and dig up some pics and post.

What kind of pump?
Electric or Mechanical?

What is your end game? Replace or rebuild?

[ckohler0529]

Mechanical. End game is a good cleaning and to learn how to service them.

[ajgaines]

I have been trying to remove the fuel pump myself and there is one bolt that is IMPOSSIBLE to remove. It's so hidden I can't even get a socket or wrench on top of it, much less remove it.

[Sam]

that's one reason why a few decades ago I by-passed my engine mounted mechanical pump with a wall mounted electric pump. I think they work better.

[capnward]

IMO, mechanical pumps work better. They don't require electricity, or an oil pressure safety switch which needs to be bypassed to pump fuel with the engine off, and have better suction than an electrical pump. The hand bail underneath them enables you to pressurize the fuel line up to the float valve, so the engine starts sooner. Using MMO in the fuel keeps them lubricated internally. The main advantage electrical pumps have is that they are easier to access and replace. It's good that you want to know how to service your mechanical pump. I serviced it once, and it didn't really need it. The pump has been perfect for 2800 hours. You will be spending a lot more time with the carburetor than the fuel pump. The best reference is the Moyer manual.

[joe_db]

I agree. I have an electric pump and would switch to mechanical in a second if my engine could have one. I will be posting a thread soon about a vapor return line and that kind of thing was never an issue with my mechanical pump back in the day.

[JOHN COOKSON]

Don't forget a fuel pressure gauge just before the carburetor when you overhaul the engine's fuel system. This is the ideal time to install one if you don't have one already.

TRUE GRIT

[SubtoSail]

On the moyer site, under support, instructions, is a PDF of the mechanical fuel pump rebuild kit. That has instructions for disassembling the pump.

As for removal, there are two bolts behind the pump portion. The forward one is probably easy to get to. The aft one is between the pump and the sediment bowl. Removing the bowl makes access easier. Loosen the nut on the bottom of the bowl, swing the arm out of the way and the bowl drops free. Be careful, it is full of gas, and the arm is the only thing holding it. Those two bolts and an inlet and outlet hose are all that attach to the pump.

Carb removal is easier. Remove the clip holding the throttle cable on, and similar for choke cable. Remove the fuel hose, and the scavenge tube: the tiny wire piece that runs from the bottom of the carb to a spot up on the block. After that its just the two bolts holding the top of the carb on. The moyer manual has carb disassembly instructions.

Good luck!

[ndutton]

Capn, that's only one side of the story. For example, mechanical pumps do something else electric pumps do not: pump raw fuel into the crankcase in the event of a diaphragm failure. They do this on purpose, it's a requirement of the USCG.

Old school automotive mechanical pumps had a weep hole in their casting that would pee fuel out when the diaphragm failed as a visual reference. No way can that be allowed into a boat's bilge because of the risk of heavier than air vapors and corresponding risk of fire/explosion so errant fuel is sent to a containment vessel, the crankcase.

I'll limit my comments to safety and save the advantages of an electric pump (fuel polishing, fuel transfer, filter priming) for another time.

Point being, there are advantages to both and it's notable that MMI offers both. However, have a look at what pump is used on their rebuilds.

[capnward]

No end of questions

That's absolutely right, Neil. I had forgotten that important issue with mechanical pumps. Pumping fuel into the crankcase when the diaphragm fails is a horrifying thought. It seems that would be only marginally safer than it going into the bilge, where you could at least smell it. That's why I am religious about putting MMO in the fuel, and not using ethanol, to keep the diaphragm in good shape. I think it has been about 20 years since I replaced it. I am still waiting for the diaphragm to fail. In the meantime, I wonder:
What would indicate gas in the crankcase, besides oil smelling of gas when you changed it? Would gas vapor come out the oil fill tube, or the dipstick? Would the dipstick smell of gas? Would the engine stop from lack of fuel, or just run differently? Would the oil pressure go down? Would gas mix into the oil, or would it separate into an explosive layer of gas on top of the oil under the crankshaft? What would happen if gas in the crankcase exploded? Do electric pumps have diaphragms? What happens if they fail?

[joe_db]

Mechanical pumps have issues too as you can see. If an electrical pump diaphragm fails it will just not work anymore. The gas is still contained inside the pump.
As for gas in the crankcase, I guess it depends on how much. With our engines that don't have a front seal it could be very dangerous, you would have gas mixing with hot oil and the fumes would be escaping into the boat

* I flew a plane once that had a valve to inject oil into the crankcase. I never used it, but apparently it was used in Alaska for parking outside on very cold nights. The gas would dilute the oil enough to keep it liquid and then when you started the airplane in the morning it would evaporate as the oil got hot.

Electric
PRO
Can be turned off to run fuel out of carb
Can run without the engine for purging and polishing
Cannot leak
You can have more than one
Available in various pressures and configurations
Easy to change out when it dies
CON
Needs electricity to work
Needs an OPSS or it can flood the carb and the boat with gas
Seem to be far more prone to vapor lock and air/purging issues

Mechanical
PRO
No electricity needed
Always turns off when the engine is off
Better suction - less vapor lock and purging issues
Simple plumbing
CON
Can leak gas into engine and it might not be obvious right away
No way to rig purge/polish system
Not as easy to swap out

[ndutton]

I am still waiting for the diaphragm to fail

Why wait for the diaphragm to fail? Why not get out ahead of it? We don't wait for impellers to disintegrate before changing, don't run out of gas before refueling.

What would indicate gas in the crankcase, besides oil smelling of gas when you changed it?

Unusually high level on the dipstick.

Would gas vapor come out the oil fill tube, or the dipstick?

Yes, once the vapor volume was greater than the available space inside the crankcase. Remember, gasoline vapor is heavier than air.

Would the dipstick smell of gas?

Yes

Would the engine stop from lack of fuel, or just run differently?

Depends on the magnitude of the diaphragm failure and if the pump still delivered sufficient fuel pressure to the carburetor

Would the oil pressure go down?

Probably but I can't say how much

Would gas mix into the oil, or would it separate into an explosive layer of gas on top of the oil under the crankshaft?

It would mix, thinning out the oil

What would happen if gas in the crankcase exploded?

I don't think this is a practical concern because there is no ignition source inside the crankcase

Do electric pumps have diaphragms?

No, something more like an oscillating piston

What happens if they fail?

Nothing other than the engine stopping. The fuel is contained inside the pump body so no external leakage and no vapor