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Author Topic: Aurelia fuel pump  (Read 614 times)
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williamcorke
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Posts: 609


B10


« on: 13 April, 2022, 09:14:25 PM »

Today I had a first run for a while in the B10. Over the winter I have swapped in a B20 (4th Series) transaxle.

First impressions of the 'box is that the gearing is a massive improvement. 1st gear has a role again! However things are not all rosy.

There's more noise that I had hoped (I checked bearings and gears visually and replaced gaskets and seals but didn't change the output bearings).

First gear looked OK but it's really quite noisy. I think I'll put up with it for a while before I decide whether to take the car apart again.

One benefit of doing the 'box swap is that it gets easier each time. And the friend who helped me lift the transaxle/brakes onto the jack before we raised it up to the underside of the car couldn't believe it only took 15 minutes and 4 bolts to secure the thing (and probably a couple more hours of joining things up before the car was drivable).

One issue left over from last year is that when enthusiastically driven the car shows symptoms of fuel starvation, which go away if you throttle back and cruise for a bit. I suspect it's a fuel pressure issue. When I tested that (2018) I got a reading of 2.5 psi, which is at the bottom of the approved range according to http://www.lanciaaurelia.info/tech-tips.html.

So here's my question: if I want the block-mounted fuel pump to produce a higher flow/pressure, should I lengthen the actuating rod, or shorten it?

I have one spare rod (the one that sit between the cam and pump actuating lever) but I'm not sure if it's a different length. Using a thinner spacer between the pump and the block would have the effect of lengthening the rod...

Any advice and accumulated lessons of experience appreciated.

Finally, here's the car this evening saying 'Drive me. But please clean me afterwards.'.





* Mads Yoga - 1 (2).jpeg (311.04 KB, 960x1280 - viewed 26 times.)
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'37 Aprilia
'50 B10
'53 B20
'68 Flavia Vignale
'55 Giulietta Sprint
S1 Land Rover
GG
Megaposter
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Posts: 490


B20 s.2, Appia C10 unrestored


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« Reply #1 on: 13 April, 2022, 09:30:01 PM »

William -
These are very tricky, and largely uncalibrated. There is the possibility of too much pressure and fuel blowing by the needle/seats and washing down the cylinder walls for premature wear. Some think that was the case back in the day.

Thinner (or no) paper will increase the rod and (I think) increase the pressure. Best to fiddle with a test gauge setup, and check at idle and higher (say 4000) rpm. When Walt Spak rebuilt my engine, I sent him three fuel pumps - he mixed and matched and tested and finally got one that he was satisfied with. So there's a ratio - 3 to make 1. Have fun.

Geoff
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B20 s.2, Appia C10 unrestored
williamcorke
Rebel Poster
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Posts: 609


B10


« Reply #2 on: 13 April, 2022, 10:16:29 PM »

The amount the actuating rod moves in and out wouldn't be affected by its length, so the variability must be in the mechanism in the pump - lever to membrane. the lever has a radial action, so there might be some 'gearing' depending on whether you were at 90 degrees to the pivot/centre or in front or behind it, I suppose.

I'd like to understand what effect experimenting with different pumps, spacer plates, rods, is supposed to produce.
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'37 Aprilia
'50 B10
'53 B20
'68 Flavia Vignale
'55 Giulietta Sprint
S1 Land Rover
chriswgawne
Permanent resident
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Posts: 1805



« Reply #3 on: 14 April, 2022, 07:29:31 AM »

I have had problems with Aurelia mechanical fuel pumps both original FISPA and new aftermarket pumps sold by bona fide Italian parts suppliers. And the problem has usually been exactly what William describes which I interpret as lack of fuel at higher speeds/revs - i.e volume related, not pressure..
I havent put measuring devices on any pumps but nowadays I only fit OE FISPA pumps to which I have fitted new membranes. I also ensure the one way flap valves are in good order.
I do also have Facet electric pumps on a couple of cars which enable me to check that the fuel starvation issue isnt anything to do with feed from the tank or the carburettor(s).
Chris
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Chris Gawne
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williamcorke
Rebel Poster
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Posts: 609


B10


« Reply #4 on: 14 April, 2022, 09:30:41 AM »

Thank you Geoff and Chris,

Chris, your comment about volume vs pressure made me think. I'd assumed that they are directly equivalent, in other words that the volume being pumped (which is relative to engine speed) will produce the pressure; more volume = more pressure. Might this not be the case? I suppose one issue could be how the pump (its valves / membrane) behaves when subject to back-pressure. When the car is running at full throttle there will, I presume, be less back-pressure (but perhaps not, this would depend on a number of factors: engine speed / gear (engine speed relative to road speed) / throttle position).

It seems that some trial and error process will be needed. I think the first step will be to take it all apart and make sure everything is in good condition. Ethanol in petrol can cause rapid deterioration as, sadly, most of us now know.
« Last Edit: 14 April, 2022, 10:01:02 PM by williamcorke » Logged

'37 Aprilia
'50 B10
'53 B20
'68 Flavia Vignale
'55 Giulietta Sprint
S1 Land Rover
GG
Megaposter
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Posts: 490


B20 s.2, Appia C10 unrestored


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« Reply #5 on: 14 April, 2022, 03:47:50 PM »

It was some time ago, but Walt reported that rod length was an issue, they were all over the place (due to wear, largely). Also that the thickness of a paper gasket could change the pump performance quite significantly. Pretty sensitive item.

Like Chris, I run a Facets elec pump (by the fuel tank) that is in series with the mech'l pump. It's used to start the car, and occasionally for high speed runs or if its super hot. But in general, the mech'l pump does just fine.
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B20 s.2, Appia C10 unrestored
Brian Long
Member
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Posts: 98

Aurelia B12, Flavia 2000 Coupe


« Reply #6 on: 16 April, 2022, 01:12:50 AM »

Exactly the same with my B12; a Facet pump for starting and the mechanical pump does the rest.
Check the pump pivot for wear; it is quite highly loaded. you can check the effectiveness of the actuating rod's stroke by carefully turning over the engine until the rod is protruding to its maximum extent, measuring the protrusion and comparing that with how far it would push the operating arm within the pump. Modifying the thickness of the insulating block would optimise the travel of the pump mechanism.
Brian
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