Mechanical fuel pump rebuild services

[Don Moyer]

After adding rebuilding kits and stainless sediment bowls to our online catalog in February and March, we continued looking into ways to make the mechanical fuel pump more reliable.

It quickly became apparent that the condition of the upper housings was the single most critical threat to the pump's reliability and safety. Approximately half of the old mechanical pumps we had stockpiled for rebuilding proved to have unusable upper housings due to corrosion, warping over the sediment bowl or hairline cracks around the inlet and outlet fittings. Developing a new and stronger upper housing therefore became central to our efforts in supporting the mechanical pump option.

With this background, if your mechanical fuel pump malfunctions, or when it comes time to rebuild the pump by virtue of age, we suggest the following progressive approach:

1. Disassemble your pump, and check the condition of the major housings. If they are in good condition, including a good fit between the sediment bowl and the underside of the upper housing, you should be able to rebuild your pump using one of our mechanical fuel pump rebuild kits.

2. If you discover that your upper housing is in good condition, except for a noticeable downward bow above the sediment bowl (where the bail attaches to the housing) which causes the bowl to rock back and forth when checking the fit without the rubber washer, you can most likely straighten this part of the housing using our mechanical fuel pump repair tool.

3. If you discover that your upper housing is not usable, but the rest of the pump is in good condition, you could opt to simply replace the upper housing with one of our new (improved) upper housings . This would be an especially attractive choice in cases where you may have previously rebuilt your pump and subsequently discovered a leak around one of the fittings.

4. If your pump looks like the proverbial "basket case", you can opt for either a rebuilt original pump or an MMI mechanical fuel pump which incorporates a new upper housing and stainless sediment bowl.

[shemandr]

fuel pump rebuild

i have the mechanical fuel pump rebuild kit. the instructions show the disassembly of the pump off the engine. i don't have good access to the engine in that area and cannot see how the pump can be taken off the engine.
the rebuild seems to require access to two bolts/screws on the bottom of the pump, removal of the priming bale and removing a pin through the diaphram post.. i can't see doing this with the pump on the engine.
how can i remove the fuel pump?

[Don Moyer]

The pump is mounted with two 1/2" hex-headed bolts. The forward bolt is usually rather easy to remove, but access to the rear bolt is restricted by the sediment bowl. If you can loosen the bail and remove the bowl, the rear bolt will be a bit easier to handle. For years I've been using a cheap 1/2" socket, which I ground quite thin around the front, to squeeze past obstructions and get to the rear bolt. I use a 3/8" extension approximately 6" long, and I've always able to get the rear bolt to turn, even though it isn't always possible to get the socket on straight.

[shemandr]

thanks for the tip. i think this is going to require an access port in the 1/4 berth locker. i glad to know what i'm after before i cut up the boat!

[Bob Grenier]

I have found that if you replace the mounting bolts with Allen-head bolts it makes replacing them a lot easier as socket clearance is no longer a problem. Also because a lot of time the back bold is done by feel only.

[shemandr]

feel only is an understatement. it took about two hours of contortionism. bleeding hands and a good patch of blue air to get that rear bolt out. i like the allen type bolt idea. thanks.

[shemandr]

one question on the rebuild of the fuel pump: since the lower housing cover came off with an explosion of springs and associated parts i did not get to examine the placement of same. i surmized from the picture that the two springs are placed, one on the rocker arm and one on the end of the rocker arm over the end of the plunger/diaphram. they then fit the hubs on the cover on the other end. is that correct? assembled this way i get a healthy squirt of gas using the priming lever, and similar noise if i engage the end of the rocker arm and push it with a screwdriver.

[Don Moyer]

I would have to say that you have most likely gotten your pump back together properly.

Don

[shemandr]

happy ending

the pump, the carbuerator and new racor filter are all installed and the engine runs smoothly. i don't know if the stalling problem is solved because that could happen after an hour or more of smooth running.
after installation of the filter, and before removal of the mechanical fuel pump and carbuerator for the rebuild, there was a gas odor. yes, i did spill gas cleaning the bowl to the fuel pump and cutting the fuel line for the filter. but it seemed like there was some gas in the throat of the flame arrester. i haven't decided if it still exists after the rebuilds. i am wondering: i put the fuel filter a bit higher than the fuel intake to the fuel pump to allow access to the bottom of the filter for draining. is the only safeguard keeping fuel from filling the float chamber, and hence overflowing into the air intake, the quality of the needle valve seat?
i could install a longer fuel line with a dip below the level of the fuel intake to discourage gravity flow from the filter when the engine isn't running. the fuel tank pick up is on the top of the tank and is above or level with the fuel pump intake.

[Don Moyer]

You really should have a manual fuel valve somewhere ahead of the carburetor, so that you can positively shut off the fuel to the carburetor while you're away from the boat. While it's true that a perfect float valve will keep fuel from collecting in the throat of the carburetor indefinitely, all it would take is a "fly-speck" piece of crud to hold the float valve open.

Regards,

Don

[shemandr]

Yikes!

that needle valve doesn't seem like enough security for my taste. one good thing about doing this myself is gaining an appreciation for issues like this. if i paid a mechanic to do this i wouldn't have given it a second thought.
there is a shut off on top of the fuel tank about six feet away. that still leaves fuel in the in the fuel line and fuel filter, which could flood the carburetor if the vacuum from the tank to the carburetor were broken. do you think i need a shutoff, say between the fuel filter and the carburetor?

[Don Moyer]

Placing a valve just ahead of the carburetor would be the most conservative approach, especially for long absences from your boat.

However, if your needle and seat has chronic problems of leaking, it would be good to know it, since a leaky float valve will lead to a rich running condition. For this reason, you may want to leave the valve just ahead of the carburetor open while you're on the boat to observe it from time to time.

[HOTFLASH]

Is valve at the fuel tank good enough?

You really should have a manual fuel valve somewhere ahead of the carburetor, so that you can positively shut off the fuel to the carburetor while you're away from the boat. While it's true that a perfect float valve will keep fuel from collecting in the throat of the carburetor indefinitely, all it would take is a "fly-speck" piece of crud to hold the float valve open.

Regards,

Don

Or is another one needed? Is there a way to regulate that valve from the cockpit without having to open the engine compartment?

[Don Moyer]

The basic concept of a manual valve sort of dictates that it would be located in the fuel line itself, and at a location that best protects the boat from a fuel leak while it (the boat) is unattended.

You could no doubt find a valve with a remote control feature to turn the fuel off and on from the cockpit during the time you're on board (an electric solenoid comes to mind), but then you'd probably still want to have a manual valve to back up the remote controlled system when the boat is unattended. I would list a manual fuel valve in the same category as a through-hull, where there's really nothing quite like "putting your hand on a valve" to give you the security you're looking for.

Best regards,

Don

[mingamells]

Fuel Pump Rebuild Kit

Currently, my fuel pressure is 5.5 psi with (apparently) the standard mechanical fuel pump. Would your rebuild kit reduce the fuel pressure to typical levels (3-4 psi)?

Thanks in advance.