Mechanical Fuel Pump Repair Questions

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Don Micheletti
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Re: Mechanical Fuel Pump Repair Questions

Postby Don Micheletti » Sat Feb 18, 2017 3:52 pm

The only reason that I rebuilt my fuel pumps was, because the car had been "resting" for near 20 years, I was afraid that modern fuel with ethanol might cause failures, or even fire.

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tyang
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Re: Mechanical Fuel Pump Repair Questions

Postby tyang » Sat Feb 18, 2017 7:31 pm

michaelbalk330 wrote:Tom, Dyke, John and menlodon, I suspect you are all correct-
I always felt my old checkvalves, and the diaphragm were OK and saved them. In fact nothing seemed that bad with the old pump except a slight gasket leak and the fact it didnt work, but the lever was a bit sloppy because the pin was a bit worn.
I just got frustrated and stopped playing around, though I definitely made progress.

you have inspired me to go at it again. I suspect with old check valves, plus the rebuild I did to make the lever mechanics strong and in spec, plus a thinner spacer it will work. thanks. Michael


Do not use the silver check valves. Even if you figure out how to install them in a fuel pump, they don't work! There's a new rebuild kit I've used that has check valves that look exactly like the original valves. I've had good results with that one. Also look closely at the seating surfaces of the nitrile gaskets. Try to face the pump body to insure a good seal between the check valves.

Tom
'63 330 America #5053

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michaelbalk330
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Re: Mechanical Fuel Pump Repair Questions

Postby michaelbalk330 » Sat Feb 18, 2017 10:06 pm

i think i used a rebuild kit from "Then and Now automotive", for Fispa 150 - same pump as flaminia, etc, but the check valves were definitely different than what was in there. for what its worth, I attached rebuild instructions from the old Ferrari of Atlanta.
LASTLY, Tom I am assuming the pic of the ones i used is of course of the ones I shouldn't use?? where can i get correct ones if i need? UGH
P1090654.jpg
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Michael
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Lowell
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Re: Mechanical Fuel Pump Repair Questions

Postby Lowell » Sun Feb 19, 2017 2:01 am

Do not use the silver check valves. Even if you figure out how to install them in a fuel pump, they don't work! There's a new rebuild kit I've used that has check valves that look exactly like the original valves. I've had good results with that one. Also look closely at the seating surfaces of the nitrile gaskets. Try to face the pump body to insure a good seal between the check valves.


My mechanical fuel pump has always not worked very well.

Tom, where do you find that new rebuild kit?
Lowell Brown
1966 Gold 330 2+2 Series II

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John Vardanian
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Re: Mechanical Fuel Pump Repair Questions

Postby John Vardanian » Sun Feb 19, 2017 2:55 am

My conclusion that a half-way-full bowl is the culprit to fuel starvation is purely based on my own experience with my car.

When the car was new to me, I noticed that the bowl was never full. Then I'd be cruising down the road and if I depressed the gas pedal just slightly to pick up speed, the carburetors would "sneeze", which is a sign of lean mixture. I guessed that the reason for sneezing was that the accelerator pumps were dry and had nothing to squirt into the throats when the pedal was depressed. I took the fuel pump apart and put it back together (more than once), rebuilt it, etc. and saw no improvement. The last time I took it apart I noticed the flat levers were upside down, which meant diminished stroke of the pump. I flipped the levers, put everything together and started the car, the bowl filled up all the way immediately. I took the car for a test drive, no more sneezing. This was 16 years ago.

Now that I have the pump apart again for restoring, I noticed my flat levers are somewhat bent. So, I figured I need to back off on the stroke a little by distancing the pump from the block.

john

PS. A pressure gauge does not tell the full story. You could get your 3psi at the fuel bowl, but if that 3psi is not purely hydraulic it doesn't do much good. Remember air can be pressurized in that little vessel just as gas can and your gauge will give you your 3psi with the bowl half empty.
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tyang
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Re: Mechanical Fuel Pump Repair Questions

Postby tyang » Sun Feb 19, 2017 8:27 am

John Vardanian wrote:My conclusion that a half-way-full bowl is the culprit to fuel starvation is purely based on my own experience with my car.

When the car was new to me, I noticed that the bowl was never full. Then I'd be cruising down the road and if I depressed the gas pedal just slightly to pick up speed, the carburetors would "sneeze", which is a sign of lean mixture. I guessed that the reason for sneezing was that the accelerator pumps were dry and had nothing to squirt into the throats when the pedal was depressed. I took the fuel pump apart and put it back together (more than once), rebuilt it, etc. and saw no improvement. The last time I took it apart I noticed the flat levers were upside down, which meant diminished stroke of the pump. I flipped the levers, put everything together and started the car, the bowl filled up all the way immediately. I took the car for a test drive, no more sneezing. This was 16 years ago.

Now that I have the pump apart again for restoring, I noticed my flat levers are somewhat bent. So, I figured I need to back off on the stroke a little by distancing the pump from the block.

john

PS. A pressure gauge does not tell the full story. You could get your 3psi at the fuel bowl, but if that 3psi is not purely hydraulic it doesn't do much good. Remember air can be pressurized in that little vessel just as gas can and your gauge will give you your 3psi with the bowl half empty.


John

I think your "Sneeze" on initial throttle can be fixed with a slight adjustment of the mixture screw. You may be running on the edge of lean, and as soon as you apply throttle, for a split second, it becomes too lean. IMHO, you're chasing the wrong problem. Now, it could be something else, but I don't think it's from the accelerator pumps. Think about it, the tube that feeds the accelerator pumps is at the bottom of the fuel bowl, for that to run dry, you would have all sorts of other problems from starving out the other jets.

Tom
'63 330 America #5053

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tyang
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Re: Mechanical Fuel Pump Repair Questions

Postby tyang » Sun Feb 19, 2017 8:30 am

Lowell wrote:
Do not use the silver check valves. Even if you figure out how to install them in a fuel pump, they don't work! There's a new rebuild kit I've used that has check valves that look exactly like the original valves. I've had good results with that one. Also look closely at the seating surfaces of the nitrile gaskets. Try to face the pump body to insure a good seal between the check valves.


My mechanical fuel pump has always not worked very well.

Tom, where do you find that new rebuild kit?


Partsource has them. Geof sold me a fuel pump kit with all the check valves and gaskets that came in a Lucite box about a year ago, and it was the nicest fuel pump kit I've seen! The trick is to get him to answer the phone!

Tom
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tyang
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Re: Mechanical Fuel Pump Repair Questions

Postby tyang » Sun Feb 19, 2017 8:44 am

michaelbalk330 wrote:i think i used a rebuild kit from "Then and Now automotive", for Fispa 150 - same pump as flaminia, etc, but the check valves were definitely different than what was in there. for what its worth, I attached rebuild instructions from the old Ferrari of Atlanta.
LASTLY, Tom I am assuming the pic of the ones i used is of course of the ones I shouldn't use?? where can i get correct ones if i need? UGH
P1090654.jpg


I was away last week, and I'm still catching up with looking at stuff, so I finally looked at your picture. Those silver check valves are the ones that don't work! You need two pairs that work in conjunction with one another. One pair only allows fuel go in one direction and the other allows fuel in the other direction. Those &*%$# silver check valves only fit in one side, and not very well, the second pair doesn't fit because the originals were different in size. When those valve were the the only rebuild kit available, I ordered only the nitrile gaskets for the old check valves and rebuilt the fuel pumps using the old valves. If the old valves weren't working, I would find good ones from old parts we kept at the shop.

As simple as rebuilding a mechanical fuel pump might be, there are a lot of little tricks. As these pumps get older, you have to check everything very closely. if things don't seal properly, or line up correctly, you're going to have problems. Did you check to make sure the sealing surfaces between the diaphragm is flat? If you don't do that, you're going to have leaks! I recently had one that we surfaced the two pump halves, and the pump STILL leaked. The original pump diaphragm was a multi layered piece which is now replaced with a single layer membrane. It may pump OK, but does a crap job at sealing the pump body. These are the stories we swap among guys who work on these cars for a living, so imagine your struggles on your car times 10!

Tom
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Don Micheletti
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Re: Mechanical Fuel Pump Repair Questions

Postby Don Micheletti » Sun Feb 19, 2017 11:57 am

One of the things a pressure gage tells you is whjether the checks are operating properly. If the gage is steady, all is OK. If the gage is bouncing around a lot, then you have a check problem.

Mine runs steady at about 4-1/2 psi.

Don Micheletti
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Re: Mechanical Fuel Pump Repair Questions

Postby Don Micheletti » Sun Feb 19, 2017 12:13 pm

On a 250 engine, here is the fuel pump gear train numbers and pump to crank cycle ratio

Crankshaft oil pump drive gear: 27T
Oil pump Driven gear: 33T
Ratio: .818:1
Fuel Pump Cam Drive Gear: 14T
Driven Gear: 47T
Ratio: .298:1
Overall Fuel Pump / Crank Ratio: .2437:1

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John Vardanian
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Re: Mechanical Fuel Pump Repair Questions

Postby John Vardanian » Mon Feb 20, 2017 2:34 am

tyang wrote:
John Vardanian wrote:
John

I think your "Sneeze" on initial throttle can be fixed with a slight adjustment of the mixture screw. You may be running on the edge of lean, and as soon as you apply throttle, for a split second, it becomes too lean. IMHO, you're chasing the wrong problem. Now, it could be something else, but I don't think it's from the accelerator pumps. Think about it, the tube that feeds the accelerator pumps is at the bottom of the fuel bowl, for that to run dry, you would have all sorts of other problems from starving out the other jets.

Tom


Tom thanks for your note. Yes, I enriched the mixture till I got tears in my eyes from the fumes. Also, on advice, I even tried on richer jets.

To your point re the accelerator pumps, I'd be driving down the road and intermittently there would be a momentary loss of power. The inertia of the car would keep the motor barely running until just enough fuel would come to rescue, then it would run fine until the next dry episode. So, to me this meant that at least one of my carb bowls went dry.

john
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