500 (Classic) Fuel pump pressure, Giardiniera

[Giardiniera 66]

I can’t seem to find any info as to the fuel pumps output pressure in psi or bars for my 1966 Giardiniera. Does anyone know what it should be? Pattern part pumps not an exact replica and I have a feeling it’s over-fuelling....Hi everyone, Ronan here in Norfolk, Uk with my 1966 Fiat 500 Giardiniera which I’ve owned since May 2016!

 

[IanEmery]

I can’t seem to find any info as to the fuel pumps output pressure in psi or bars for my 1966 Giardiniera. Does anyone know what it should be? Pattern part pumps not an exact replica and I have a feeling it’s over-fuelling....Hi everyone, Ronan here in Norfolk, Uk with my 1966 Fiat 500 Giardiniera which I’ve owned since May 2016!

I wonder if your experience of over pressure is, in fact, a leak past the carburettor fuel flow needle valve? What symptoms does the car show? Fuel leaks or perhaps rich running? I was chatting to another Giardinera owner who had fuel leakage problems last year and that turned out to be needle valve trouble. On the ‘normal’ 500 engine it is possible to alter the amount of petrol pumped per stroke by changing the number of gaskets under the fuel pump, I’m not sure if it’s the same on the Giardinera engine but it maybe possible that gaskets have been removed prior to the pump being replaced, trying to delay replacement, and this has given the new pump a longer pump stroke. You could try increasing the number of gaskets to see if this cures your problem.

I live on the Suffolk/Norfolk border in Oulton Broad so if you live on the east side of Norfolk maybe we’re not too far apart. If you don’t wish to say whereabouts you live on open forum by all means reply by PM.

 

[Giardiniera 66]

I wonder if your experience of over pressure is, in fact, a leak past the carburettor fuel flow needle valve? What symptoms does the car show? Fuel leaks or perhaps rich running? I was chatting to another Giardinera owner who had fuel leakage problems last year and that turned out to be needle valve trouble. On the ‘normal’ 500 engine it is possible to alter the amount of petrol pumped per stroke by changing the number of gaskets under the fuel pump, I’m not sure if it’s the same on the Giardinera engine but it maybe possible that gaskets have been removed prior to the pump being replaced, trying to delay replacement, and this has given the new pump a longer pump stroke. You could try increasing the number of gaskets to see if this cures your problem.



I live on the Suffolk/Norfolk border in Oulton Broad so if you live on the east side of Norfolk maybe we’re not too far apart. If you don’t wish to say whereabouts you live on open forum by all means reply by PM.

Hi Ian and thank you! I’m in West Norfolk, in Gayton near Kings Lynn.
I’ve had various issues with the fuel system and last year I rebuilt the carburetor with a kit from Ricambio. I also jumped at the chance of a used Weber 26.OC carb spare on eBay as they are getting really rare. I still have the pump the car came with which is the original style one but it was leaking engine oil from the clever diaphragm which had failed from the pushrod side. I ordered a same type original pump from a well known supplier but they shipped me the cheaper Eastern European part...., they did refund the difference after I contacted them. There was an assortment of gaskets including some rubber ones on the original installation. The car continued to leak oil from the spacer joins until I was doing engine rebuild number two in 3 months..... ( spark plugs needed helicoiling, stupidly didn’t get both done the first time[emoji21][emoji21][emoji21]) and I had several sets of gaskets in stock for petrol pumps.
The reason I ask about the fuel pump pressure is I’m a fan of Heidi and Frannys garage on YouTube and the very thing you mention of using gaskets to counteract pump stroke was the topic of another air cooled car, the VW Beetle that they look after for a friend. They knew the optimum pressure for the VWs carb was about 2.5/3.0 bar for example, but the available replacement pump was kicking out up to 8.0 bar and forcing fuel past the float needle valve. They elected that as the new pump ran correctly without having to guesstimate the pressure reduction via extra gaskets and shims, to fit a pressure regulator in line after the pump and before the carb. This is a simple single in, single out regulator with a dialable pressure adjustment knob which is a simple fit but what I can’t seem to find is the optimum pressure the Weber 26.OC carb actually likes to operate at? I have an old blue 500 Main Dealer workshop manual, an autopress manual, an original English language Giardiniera handbook and the Olyslager 500 motor manual. All are very short on the Petrol pump info and nowhere can I seem to find what it potentially was. I’m assuming the standard 500 pump will have the same output as the basic functions and engine rpm are the same.
Hurrah! I’ve reached the end of my diatribe!

 

[Giardiniera 66]

Apologies! As to what’s been happening.... car runs great and fast, timing is all good but does seem to dully backfire on switch off and some seeping of fuel around the carburetor, it has run with this carb since I bought it, I took great care in setting the float and needle valve has got its aluminium washer in place. I love this car so much and I’ve managed 2,840 kms since May 2016, considering it’s garaged but road ready in the winter and there’s four other special cars to play with!

 

[IanEmery]

It sounds like you’ve been having some fun and games with it, Ronan. I’ve got most of the books you list and the only detail I can see is the stroke of the pump control pushrod. The only person I can think of who might know the fuel line pressure would be Tom aka The Hobbler but I think even he would be unlikely to have this info. I would think you are right to assume pressure details would be the same for both vertical and horizontal engines. Good luck with your quest

It’s a shame we’re so far apart geography but, who knows, we may be on the same road one day.

I have to say I had never seen or heard of Heidi and Franny’s garage but I just took a look and it looks like it could be interesting, thanks for that

 

[the hobbler]

Looked through all my sources of technical information, nothing to advise what the PRESSURE should be---all I can find is the pump OUTPUT--5.5 gallons/25 litres per hour (which I reckon will be about 1.5/2.0 psi). When checking the pump actuating rod movement, there should only be between 1.0 and 1.5mm of rod protruding past the gaskets when the actuating rod is fully out. Don't forget that you will have to turn the engine over TWICE to get the full range of rod movement (cam-driven, so only 1/2 engine speed). This adjustment is controlled by the number of gaskets between the pump and the mounting point. Sorry I can't be of more help. :bang:

 

[Giardiniera 66]

Aha! Great reply! This gives me some hope and a good base to start from! I know I may be over engineering the problem with the thoughts of a pressure regulator but with a simple pressure test a lot could be revealed. It would be better if I could rebuild the original pump with a service kit but I don’t think these are available. The original had the brilliant middle void in the red section of the diaphragm which had a tiny drain hole facing the ground when the pump was in situ, meaning if the petrol side failed, or the engine oil side failed, the two liquids didn’t cross contaminate!