TA 0844, first registered September 1936, was purchased as a wreck but with the original MPJG engine. The original carburettors had been replaced with aluminium alloy bodies, aluminium piston chambers and obviously non-standard furniture. One body was missing the ear for the choke spring, the other the lug for the suction chamber retaining screw. Over the years I have managed to acquire a pair of bronze bodies and many small parts. The details below relate to my attempt to sort out carburettors which match the year the car was first registered.
The carburettors are of the HV3 type, specification AUC 327 for the year 1936. The photos A and B show the layout. Specification AUC 374 was from 1937 to 1939. Bronze or alloy bodies 1945 are available as authentic reproductions as are the right handed twenty degree float chambers AUC 3495 and float chamber lids, casting no.1161 (AUE 997). Suction chambers ABF 399 with matching pistons AUC 3175 made from alloy are available but are expensive. Bronze chambers and pistons are no longer made.
The exploded view of a typical HV carburettor is shown in drawing 1. For a TA the choke lever shown is incorrect. The choke lever connecting bar and the float chamber hold up bolt are a much later variant. A more modern weighted piston is shown. A twin carburettor layout is illustrated on page 14 of The Parts Manual for The MG Midget Series TA and TB showing the correct choke lever connecting bar.
The connection between the carburettor spindles was a flexible spindle, AUC 1236, with brass split sleeve links no. AUC 1924 Type 3. These have nut and bolt clamps. This was changed at TA1876 to a solid brass connecting bar with the same links. For the TC specification AUC 429 the solid connecting bar was used but ‘concertina’ style links AUE 75 were used.
photo A
The choke lever connector was as shown in photos B and D, which is a steel rod with spring loaded brass end joints screwed on. Locknuts fix the position. Those shown are adjustable for length and tightness of ball joint, they are no longer available. A variant of these is similar, made of brass, but with non-adjustable joints. Photo D shows three types of choke lever connector and the non-adjustable joints. A very early connector is shown made of steel with fixed lever bolts. The TA style connector is shown in the centre. This style was changed at TA 1877 to the forked end type with a tapered boss and locknut, ABF 295. This latter type was also used for the AUC 429 carburettors on the TC. There is a much later variant of the forked type, which has just a fork and nut without a tapered boss and is numbered AUC 2256.
The accelerator pedal shaft to throttle spindle connector is shown in photos A and E. The top connector in photo A is a type used on cars from the 1930’s to the 1950’s. It has spring loaded non-adjustable ball joints and is made from steel. The lower connector has similar brass ends to the choke lever connector shown in the middle of photo D.
An early float chamber to body bolt no. AUC 1541 is shown in photo C and again in more detail in F top. This early bolt has a groove into which fits a cork seal number AUC 1542. The later bolt, which has the same number, AUC 1541, shown in photo F bottom and in the exploded view, uses a plain fibre washer AUC5207, brass washer AUC 5026, fibre washer AUC 5207 sandwich between the bolt and the float chamber. Both use the same sized fibre washer between the float chamber and the body AUC 2130. The groove on the early bolt can be machined flat to accommodate the later sandwich of washers if AUC 1542 is unobtainable.
photo B
The bull nosed float chamber lids, casting no.1161, originally had airvent grooves in the fixing nut boss. On 18/02/1936 the works specification was changed, the air vent grooves were machined out. A slightly different banjo airvent assembly was fitted, comprising lid fixing nut AUC 1867, aluminium washer no. AUC 1557, the overflow pipe banjo and then serrated fibre washer no. AUC1928. The later lid, casting 4261, will also fit. The gasket between float chamber and lid is AUC 1147.
The overflow banjos with pipes are AUC 3202B (front, polished) and AUC3203B (rear, polished). Pipes are 19inch and 25inch, plated versions are available as are short pipe versions.
photo C
The cap on the piston chamber was made from brass, with a circular top and a knurled edge no. AUC 2144SBO. A coin slot is machined across the middle and the words ‘Use Bicycle Oil’ is engraved on it. A fibre washer was used no. AUC 4900. There are at least six variants of this cap made from brass and a few others from black plastic.
Wear in the bearing surface of the butterfly spindles can be rectified in two ways: the spindle holes can be line bored to take steel sleeves with an internal teflon coating. Standard 5/16inch diameter spindles can then be used. Alternatively spindles which are oversized can be used with suitable boring, they are 8mm diameter. As most wear occurs on the spindle a replacement standard spindle may be sufficient.
photo D
The piston. for specification AUC 327 was made from brass. This was changed for specification AUC 374 to aluminium. Burlen Fuel Systems quote this piston no 3175 as not requiring a spring. The piston shaft was solid i.e. no damper.
photo E
The slow running spring as for a TC is shown in the drawings no. 2 and 3, the TA spring is the same, as shown in Photos B and C. The method of attachment for the upper part is with a small bracket for the TC which is fixed to the carburettor flange. For the TA, I have copied an odd part which has a hole for the cable outer partly through it and a hole for the inner completely through. A splitpin and washer was used to secure it to something. I made this with a ¼ inch BSF thread and secured it to a small plate using the inlet manifold mounting bracket bolt, see photos A and B. For the lower attachment of the spring I have bent the end of the spring at right angles to fix across the slow running lever as shown in drawing no.3. In the photos a piece of welding wire serves as a dummy slow running cable inner.
photo F
Size.183mm.
Body 1945, Bronze or Gunmetal.
Stud dia.13/32 in.
Stud centres. 65mm.
Float chamber 1891 Gunmetal.
Float WZX 1303
Float chamber size. T2, 2.3125 ins diameter.
Float chamber lid, casting no.1161.
Float chamber to lid gasket AUC1147
Fuel Inlet Banjo bolt. AUC 2698. Fibre washers AUC 2141.
Float chamber lid fixing nut. AUC1867.
Overflow banjo top washer AUC1557.
Overflow banjo serrated washer AUC 1928.
Tickler pin kit WZX 993.
Tickler pin 1249.
Overflow banjo and pipe front. AUC 3202B. (19ins. Long).
Overflow banjo and pipe rear. AUC 3203B. (25ins long).
Hand throttle lever. 3033. Adjusting screw and spring kit WZX 982
Throttle lever LH side of rear carb. AUC 2374.
Throttle stop LH side of front carb. AUC 2199.
Jet lever front. 3006. with 17/64in hole. This dimension depends on the size of the lever connector joints used and can be smaller as AUC 3007.
Jet lever rear. 3089. with 17/64 hole. This dimension depends on the size of the lever connector joints used and can be smaller as AUC 3097.
Jet link front. AUC 2382.
Jet link rear. AUC 3096. (Now AUE 64)
Jet AUC 8182. Size 0.090inch.
Throttle spindle front, long end LH side. AUC 1398.
Throttle spindle rear, long end RH side. AUC 3009.
Flexible spindle. AUC1050 (shorten if return spring on rear carb).
Return spring RH side front carb. AUC 3351.
Collar RH side front carb. AUC 1380.
Sleeve RH side front carb. AUC 3350
Piston to 15/1/37, 983.
Piston. after 15/1/37, 3175.
Piston chamber top AUC 2144SBO
Slow run gap 0.01in to 0.04in.
Needle (weak) S, AUD 1316
Needle (standard) AC, AUD 1034
Needle (rich) M1, AUD 1267
Modifications
Suction chambers changed from bronze to aluminium at TA 1925
Float chamber overflow seals were changed on 18/02/1936.
Connecting rod 1851 deleted 17/4/36 Used only for the first few pairs of carburettors.
Jet needle. From L to S. Factory 22/7/36
Overflow pipes changed to 3202 Factory 23/7/36
Jet needle From S to AC. Factory 19/9/36
Piston From 983 to 3175. 01/02/1937. ( Piston 3175 made from aluminium weighs 7.5ozs with needle and needle fixing screw).
The brass piston for export cars changed to 3188. Weight 7 ½ ozs.
At chassis no. 1876, Throttle linkage changed to TC type.
Cork
seals number AUC 1542, suction chambers ABF399 and matching pistons
AUC 3175, spindles ( to be cut to the correct length) and other parts
can be obtained from Burlen Fuel Systems, www.burlen.co.uk
. Tel01722412500.
Oversized spindles and other parts can be obtained from
Southern Carburettors & Injection, www.southerncarbs.co.uk
. Tel 02085402723.
Jet
levers AUC 3007 and AUC3097 are listed in the Burlen catalogue.
Thanks to the MGOCC for the drawing of the slow running
lever spring.
Bob Butson, March 2010