Re: Zel's Fleet Blog...Citroen, Mercedes, Sinclair & AC Model 70
Posted: Mon Nov 20, 2023 11:02 am
Zel,
I don't think I've ever come across a low-pressure carburettor (SU) set-up fitted with a return to tank pipe.... SU's in later years were often installed contrary to the companies recommendations.....
I have, somewhere, an SU "bible" from the 1960's where it states that the maximum float chamber delivery pressure should not exceed 1.5psi on HS2 and HS4 and 2psi on HS6 versions and that they should never be fitted with mechanical fuel delivery systems....
SU electric pumps were/are supplied in 2 versions, a 1.5psi "puller" pump for use where the pump is located in the engine bay (i.e. Morris Minor) and a 2.5psi "pusher" where the pump was located at the rear of the vehicle near the fuel tank. I've no experience of the Hardi pumps but would guess they are similar. All mechanical pumps tend to operate between 4psi and 8psi. I eventually binned the SU carb for a Weber though - got tired of regular fuel leaks!!!! Webers been on there for 25 years now - no issues whatsoever.
The SU "bible" also goes into great length about how to convert your Austin A30/35 or Standard 8/10 from the original Solex or Zenith to SU HS2....
A Reliant Rebel (Zenith carb) I owned back in the '70's, went up in flames (at a set of lights on the old A1 at Sandy in Beds), when the output pipe on the AC mechanical fuel pump popped out, showering the distributor with petrol!! Hence when I acquired my present Kitten, the first thing I did was remove the mechanical pump and fit an SU one.
Is it possible that the return pipe fitted to your car is maybe for the fuel injected version? Or is indeed actually necessary? If its as blocked as it seems to be maybe it has always been blanked off.....
John
I don't think I've ever come across a low-pressure carburettor (SU) set-up fitted with a return to tank pipe.... SU's in later years were often installed contrary to the companies recommendations.....
I have, somewhere, an SU "bible" from the 1960's where it states that the maximum float chamber delivery pressure should not exceed 1.5psi on HS2 and HS4 and 2psi on HS6 versions and that they should never be fitted with mechanical fuel delivery systems....
SU electric pumps were/are supplied in 2 versions, a 1.5psi "puller" pump for use where the pump is located in the engine bay (i.e. Morris Minor) and a 2.5psi "pusher" where the pump was located at the rear of the vehicle near the fuel tank. I've no experience of the Hardi pumps but would guess they are similar. All mechanical pumps tend to operate between 4psi and 8psi. I eventually binned the SU carb for a Weber though - got tired of regular fuel leaks!!!! Webers been on there for 25 years now - no issues whatsoever.
The SU "bible" also goes into great length about how to convert your Austin A30/35 or Standard 8/10 from the original Solex or Zenith to SU HS2....
A Reliant Rebel (Zenith carb) I owned back in the '70's, went up in flames (at a set of lights on the old A1 at Sandy in Beds), when the output pipe on the AC mechanical fuel pump popped out, showering the distributor with petrol!! Hence when I acquired my present Kitten, the first thing I did was remove the mechanical pump and fit an SU one.
Is it possible that the return pipe fitted to your car is maybe for the fuel injected version? Or is indeed actually necessary? If its as blocked as it seems to be maybe it has always been blanked off.....
John