Carburetter Service - Matchless 46/G3L 1946 Maintenance Manual And Instruction Book

53 OVERSIZE PARTS A N D RE-BORING CYLINDER BARREL
Pistons and rings, .020" larger than standard, are available. This degree of oversize is
such that it is essential for the cylinder barrel to be re-bored to accommodate it. We
can provide chat service at prices quoted in the Spares List.
On the 350 c.c the cylinder standard bore is 2.7187 ± .0005". The 500 c.c. cylinder
standard bore is 3.250 ± .0005".
When the wear at the top of the barrel reaches .008" the barrel should be bored out
.020" oversize and a new oversize piston and rings fitted.
Crankpin rollers .001" larger than standard can be supplied. We recommend only
skilled mechanics should fit these because it is almost general that the big-end journals
and sleeves require " lapping " to ensure a correct fit.
54 WORKSHOP SERVICE
Motor cycle repairers may require service information other than that detailed in
Paras. 36 to 53 and, in those cases, our Service Department will always be pleased to
assist on receipt of details of the required matter.

CARBURETTER SERVICE

The information given in this section includes all that will normally be required
by the average rider.
racing and the use of special fuels, we refer the enquirer to the manufacturers
of the carburetter, Messrs. Amal Ltd., Holford Works, Perry Barr, Birmingham.
Our Spare Parts Department does not stock every part of the Carburettor but confines
its stock to those parts that, from time to time, may need replacement as the result
of wear. Those parts include float chamber floats and needles, jet taper needles, needle
jets and washers. For all other parts application should be made, through the local
dealer, to the manufacturers.
55 CARBURETTER FUNCTION
The petrol level is maintained by a float and needle valve and, in no circumstances,
should any alteration be made to this.
valve, the part should be replaced with new.
seat).
The petrol supply to the engine is controlled, firstly, by the main jet and, secondly, by
means of a taper needle (see 6, Illustration 14) which is attached to the throttle valve
and operates in a tubular extension of the main jet.
The main jet controls the mixture from three-quarters to full throttle, the adjustable
taper needle from three-quarters down to one-quarter throttle, the cut-away portion
of the intake side of the throttle valve from one-quarter down to about one-eighth
throttle, and a pilot jet, having an independently adjusted air supply, takes care of the
idling from one-eighth throttle down to the almost closed position. These various
stages of control must be kept in mind when any adjustment is contemplated. (See 18,
Illustration 14, for location of the pilot jet air adjustment screw.) The pilot jet consists
of a small hole drilled in the choke, or jet block.
For further details, particularly those connected with
In the event of a leaky float, or a worn needle
35
(Do not attempt to grind a needle to its