THERE ARE SEVERAL THINGS TO CHECK WHEN BUYING A SECONDHAND CARBURETTOR

[Reprint from South Wales A7 Club Magazine - Dec >99]

ONE - Is it Austin Seven?

  The originals were generally (but not all) marked >7' on the flange that bolts the carburettor or to the manifold and also C‑548 on the float chamber cover.  The Austin 10 looks the same but should be stamped on the flange >10'. Check the size of the choke tube. The Austin Seven is 17 mm, the Austin Ten is 19 or 21 mm and this should be marked on the casting at the entrance of the choke. If the choke cover is on it can be difficult to check the choke tube size.

TWO - Check that the carburettor is complete and nothing is broken.

   Check flange with throttle in fully open position as this is often broken.

THREE  - Check the banjo bolt thread where it secures the petrol pipe to carburettor.

   Check threads of bowl where they hold the bowl to main body.

FOUR - Check spindle in body.

   If loose it can be repaired. Burlen Fuels will rebore and fit a new spindle and butterfly disc for ,32 + VAT. Spindles and discs cost ,6 each. (See Roger Ballard)

FIVE - Check choke flap spring.

  If it is broken it can be replaced.

   I believe from my experience, the following is the difference in the carburettors, but I have not any information to confirm this:

- There would appear to be two types of 26VA carburettors.

- The design at the top of the barrel (or body) is different.

- The passages at the air regulating screw are different.

- There are two types of bowls, deep and shallow.

- These bowls could have been changed.

   I suggest that the earlier carburettor has the single airway at the top of the body and it is fitted with the deeper bowl. The Zenith spare parts schedule shows the shallow bowl fitted to the body with airways which are straight, one at right angles

1932 V type Carburettor - Removable choke tube and different choke control. Choke cable does not operate throttle linkage.

Later 26VA Carburettor - Type fitted with deeper bowl.

Ruby 26VA Carburettor - Type fitted with shallow bowl.


THERE ARE SEVERAL THINGS TO CHECK WHEN BUYING A SECONDHAND CARBURETTOR - PART II

[Reprint from South Wales A7 Club Magazine - Dec >99]

   Jet Sizes    (mm)  

Carburettor                     26VA              30VEI                 30VEI              30VEI

                                       -                  65 Sports@            Nippy@             Speedy@ *

 

Choke Tube                      17                      21                    21                     25

Main Jet                        0.57                  0.95                    0.85                  1.20

Comp Jet                       0.50                 0.40                    0.55                  0.40

Slow Running Jet           0.60                 0.60                     0.60                  0.60

Progression Jet             0.50                  -                          0.90                  0.90

Needle Seating             1.5                    1.5                      1.5                        -

Capacity Tube              2                      2                                  -                 2

 

*NB In the above table I have entered all sizes correctly as millimeters. However, traditionally, the jet sizes should be named A57" for 0.57, A95" for 0.95 etc. (see article below) but I found it all too confusing!

 

From PRACTICAL AUTOMOBILE ENGINEERING (OLDHlMS)

 

CARBURETTOR JET SIZES

 

   First it is to be noted that in a car or lorry engine practice, carburettor jets are graduated in diametrical measurements of the metering orifices, the progressive numbers varying generally in hundredths of millimetres ‑ one millimetre being called 100. In speaking, for example, of a 90 or 95 jet,  0.90 or 0.95 of one millimetre (namely 100) is meant and in a similar manner for a 115 or 120 jet, 1.15 or 1.20 millimetres is meant respectively.

 

CARB. JET SIZES APPEAR TO BE .002 PER 5 OF JET

 

jetsize      thou.ins.          nearest        jetsize         thou.ins.      nearest 

                drill sizes                                                                    drill sizes

40                016                   1/64 or 0.40mm 85         85        034      77 or 0.85mm

45               018                   77 or 0.45mm                90         036      64 or 0.90mm

50               020                   76 or 0.50mm                95         038      62 or 0.95mm

55               022                   74 or 0.55mm                100       040      60 or 1.00mm

60              024                   73 or 0.60mm                105       042      58 or 1.05mm

65              026                   71 or 0.65mm                110       044      57 or 1.10mm

70              028                   70 or 0.70mm                115       046     56 or 1.15mm

75              030                   69 or 0.75mm                120       048    3/64 or 1.20mm

80             032                   67 or 0.80mm

 

   Thanks to David Burris for researching these articles on the Zenith Carb from material left to him by the late Reg Picket. Alf Edwards and David who used to work with him encouraged him to write down his great knowledge of Austin 7s. He gave David a great deal of information which will be passed on to us from time to time. Reg contributed to AThe Austin Seven Manual@ by Doug Woodrow. However, David did ask me to point out that his own knowledge of carburetion is very limited so please don=t ask him anything technical!