Carburettor

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The original Amal carburettors had brass bodies and separate float chambers, and were known as types 4, 5, 6 and 29. They were fitted from 1929 until 1933 when the body material was changed to zincdie cast alloy. These were known as types 74, 75, 76, and 89, and can be distinguished from the later types because these have four air holes around the base of the body which the next type do not. In 1939 types 274, 275, 276 and 289 were introduced; these have two internal primary air passages in the base of the jet block. A later version with an ‘R’ suffix denotes that the primary air passage hole was moved to the air intake.

1955 saw a completely new carburettor being manufactured, which had the float chamber, cast in one piece with the mixing chamber and called the ‘Monobloc’, these are types 375, 376, and 389. This was fitted to the Colt on and after LA 966.

Each type number mentioned above indicates a different size of casting. Each casting was to any one of several bore sizes. Therefor when searching for a replacement carburettor, the bore or choke sizeis needed in addition to the type. The suffix shown after the type on the flange indicates which jets, float chamber and to which machine it was originally fitted, it is irrelevant providing the body is of the correct size and type and the correct jets etc are used.

Poor starting and erratic tickover is usually caused by wear between the throttle valve and the body. Fitting a new slide in a worn body is like fitting a new chain to old sprockets, a waste of time. Wear is likely to be apparent as early as 5,000 miles, but can be rectified by boring the body oversize and fitting a sleeve to the slide. The materials used in this process will last a lot longer than the original. This is preferable to fitting a non-original later type of concentric carburettor. The new Monobloc carburettors that are now available have improved materials. The prices for re-sleeving are given in the price list by RES169 or RES170 for a complete overhaul.
Or replace the basics and seals with our overhaul pack here (monobloc only)

Carburettor Settings List

A standard needle jet is used on the type 6 models unless a size is given. Standard needle jet on the Monobloc is .106. Standard needle jets are not usually marked. The needle position is the number of grooves from the top.

This was fitted to the Colt on and after LA 966.

275 Type 6 Carburettor 1954