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I´ve had some trouble with the fuel delivery with my mechanical fuel pump on my twin Dellorto DHLA 40 carbs.
Right now the car has no fuel regulator (I bought it that way) but an online fuel filter. My mechanic found an original fuel filter/regulator that we installed but the car stumbled above 3000rpm so I suspected a fuel delivery problem.
I measured the fuel pressure after the regulator and found 3.5psi, which is good for low rpms but caused the stumble of the car at higher rpms.
I wanted to know the pressure the pump was giving before the regulator, and I measured almost 7psi, at low and high rpms. My mechanic told me that at idle the carbs were overfilled, we looked at the needle valves and they were worn so I am buying new ones.

Seemes that the regulator lower pressure by half, I haven´t found any screw to regulate the pressure on the outside casing, only a little hole that seems a breather.

I think 7psi is too high for the Dellortos so I want to change the fuel pump and use the regulator. I don´t know if this is the way to go, or buy an electric fuel pump (I´ve seen 4-7 psi) and install an online fuel filter (I think this would give some more hp).


Help would be appreciated.
 

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Hello Ennio !

On the original euro filter / regulator there is a small brass screw for adjusting the pressure in the top of the assembly. According to my manual the pressure measured with a in line pressure gauge should be 3 - 5 lb / sq in. If you want to check the delivery rate of the pump, it should be approx 24 gall / hr at 2500 - 3000 rpm (free flow), and with a delivery pressure of 2.8 lb / sq in it should give approx 13.2 gall / hr. Too high pressure will ruin your needle valves as you already know. Hope this is any help for you and your Alfa Romeo.
 

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Hi Ennio,

Here is picture of a FISPA Regulator/Filter, it also has a one directional in-line thing, lets the fuel come to the regulator but stops it going back to the fuel tank, maybe this thing also regulates the pressure too.

Rich
 

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