330GT mechanical fuel pump troubles

[Lowell]

About 6 months ago, I bought an old inexpensive car (not a Ferrari) and put it up on my lift to fix things. I still have one more brake to fix.

At that time we noticed that the mechanical fuel pump on my 330GT we leaking gas. We removed the gas from the tank, put the front up
on jack stands, removed the left front wheel, and I removed the pump and put if on a bench where it sat for 6 months.

This week I finally found time to work on it. I got a repair kit that had a new diaphragm and new rubber washers to place under the delicate check valves,
I carefully removed the inlet check valves and put the new washers under them and then did the same for the outlet valves. The washers for
one pair were somewhat thicker than the old ones. In hindsight, I do not think that this needed to be done. I noticed that the mating surfaces of
the two fuel pump parts were far from flat, so I sanded them with 220 wet/dry paper on a flat mirror surface, being careful to clean them well
afterwards. I then put in the new diaphragm and clamped its rod so the diaphragm surface was flat and wrinkle free when I screwed the two pump
pieces back together. Today, a friend came over and we put the pump back on the car and filled the tank with 2 gallons of gas. With the usual procedure
of using the electric fuel pump, we started the car and let it run for several minutes before turning the electric pump off. After a few minutes, the
carb bowls emptied and the car stopped. Thinking that there might be air in the gas lines or that the pump need to be primed somehow, we added another
2 or 3 gallons of gas, replaced the wheel, and took the car off the jack stand to make it level. Starting the car with the electric pump, it again stalled
after the electric pump was turned off.

Anyone have any suggestions to what to do next?

In my compulsion to fix the mechanical pump, I did, in fact, buy two repair kits. The one that I did not use contains new check valves. I did not use these
because they are somewhat different that the old ones. Should I drain the gas tank, remove the pump, put in the new valves, and do it all over again?

Yours in frustration.

[John Vardanian]

Hi Lowell, look at the pair of tabs again and make sure they are not upside down.

john

[Lowell]

Hi Lowell, look at the pair of tabs again and make sure they are not upside down.

john

John,

By tabs I take it you mean check valves.

Although the intake and outlet valves look similar, that have slight differences in the groves in which the rubber gaskets go.
So it is harder than you think to make them topsy turvy, I think.

But do not underestimate the things that I have screwed up in the past, so that the number of mistakes that I can make is
larger than the set of integers. (I believe that there is such a larger set.)

Lowell

[250GT]

The overhaulkit doesnot provide a new "hammer" this part can be heavy worn ,and dont have the right "reach" any more.
this can be corrected by sanding down the brown spacer.
Here a pic from this side (TY) with the IMPORTANT valves position (suck and push).
Almost everyhing about this issue has been told in older posts.

C.

[tyang]

Hi Lowell,

Sorry to hear about your frustrations. These mechanical pumps are a PITA! I always end up smelling like gasoline after fiddling with one of these units!

One down and dirty method to make sure the check valves are working properly is to blow or suck on the inlet/outlet openings of the fuel pump to make sure the check valves are working. Obviously, the pump has to be removed, and most of the gasoline drained before you put your mouth to the unit! You can sometimes get the mechanical pump out of the car without draining the tank if you elevate the front of the car high enough so the tank level is lower than the inlet of the mechanical pump. I've done this with about 1/4 tank of fuel.

Another trick is to plug the inlet of the fuel rail from the mechanical pump so only the electric pump feeds the carburetors. Take the line from the regulator that comes from the mechanical fuel pump and feed it into a container. Run the engine, and watch for fuel coming out of the line from the mechanical fuel pump. It should spurt with some decent flow. If there isn't enough flow, and the pump has been checked, you may have to see if there is enough travel in the push rod. There is only about 3-4mm of total travel (bad design) to move the diaphragm so making sure there is no play between the pushrod and the pump is crucial for efficient pumping. Sanding down the phenolic spacer may be required.

Good luck!

Tom

[John Vardanian]

Hi Lowell, these are the tabs I mentioned. This photo is on this forum somewhere, as we have discussed this issue on another thread. You may want to search it.

john

[Lowell]

Hi Lowell, these are the tabs I mentioned. This photo is on this forum somewhere, as we have discussed this issue on another thread. You may want to search it.

john

I did not change those little levers or "tabs'.

Lowell