Monobloc Carburettor

Carburettor Problems

Poor starting and erratic tick over 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 found under RES169 or RES170 for a complete overhaul. Or replace the basics and seals with our overhaul pack here (monobloc only)

Monobloc carburettor settings chart

1955 saw a completely new carburettor being manufactured, that had the float chamber cast in one piece with the mixing chamber and called the ‘Monobloc’, these are types 375, 376, and 389. Each type number indicates a different size of casting. Each casting was machined to any one of several bore sizes. Therefore when searching for a replacement carburettor, the bore or choke size is 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. The swinging arm models were always fitted with air cleaners connected by a rubber hose to the carburettor.

Mixing chamber tops can have one, two or no threaded holes for cable adjusters; there is an adjuster on the carburettor OR in the cable, not both.

For jetting application please select your bike make from the following list.

Ariel, BSA,