DECARBONISATION
Decarbonising is extremely simple and should be carried out at regular intervals of
about three thousand miles (5,000 km.) if consistent results are to be expected. The
symptoms indicating an excessive deposit of carbon are undue roughness of the
engine and a tendency to pink under load, erratic running with excessive four and
eight stroking, and an appreciable falling off in power. This latter item is particularly
noticeable when the exhaust port becomes fouled with carbon as it causes an
obstruction to the free escape of the exhaust gas, and interferes with the correct
scavenging of the cylinder which is so necessary for the efficient transfer of
combustible mixture from the crankcase.
Silencer
The silencer is fitted with a detachable end cap held in position by a single nut.
When this is unscrewed the cap can be removed and the internal baffles which are
mounted on a central tube, can be withdrawn for cleaning. This should be carried out
at the same time as decarbonisation of the engine. When reassembling, make sure
that the copper sealing ring is in position before replacing the end cap, and that the
plain washer and the spring washer are replaced on the stud before tightening the nut.
Removal of Cylinder
First turn off the petrol and detach the petrol pipe at the carburetter. The pipe is
affixed to the petrol tap union and should not be disturbed. Next, disconnect the air
cleaner hose and remove the carburetter from the cylinder flange still attached to its
cables and tie back out of the way. The exhaust pipe must also be disconnected by
releasing the union nut at the front of the cylinder barrel using a “C” spanner for this
operation. If this nut should prove unduly obstinate, a few drops of penetrating oil
should be applied to the threaded portion immediately above the nut and a little time
should be allowed for this to act before attempting to unscrew the nut. Remove the
whole exhaust system. Disconnect the high tension lead from the sparking plug and
unscrew the latter.
The cylinder head and barrel are attached to the crankcase by means of four long
studs, and when the four nuts on the top of the cylinder head are removed, the head
and then the barrel can easily be lifted clear. Removal of the cylinder barrel is greatly
facilitated if the two petrol tank front locking bolts are unscrewed so that the tank can
be raised slightly and it will also be found beneficial to slacken the two crankcase
joint screws immediately below the bottom fin on the barrel. Take care when
removing the barrel to support the piston as it emerges from the end of the bore to
protect it from damage as it comes clear.
Removal of Cylinder
(Bushman)
Due to the high ground clearance provided on these models, it is necessary to remove
the petrol tank prior to removal of the cylinder. The tank is bolted to the frame at
front and rear connections and the tap and pipe can be left in position on the tank.
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