BSA Winged Wheel W1 Instruction Manual page 14

oxtremely simple matter, easily camied out even
by the most inexperienced novice if the following
instructions a.re observed.
The íorrna,tion oí carbon deposit is inevitable
inside the combustion chamber, and a,t certa,in
other pla.ces, in a.ll internal combustion engines,
because it is either the by-product oí the process
o£ combustion, or a residue from the temperature
eÍÏect on the lubricating oil, or both. If the com-
bustionable mixture from the carburetter is a little
on the rich side, due to the use oí too large a jet,
or to urinecessarily long periods oÍ "ming with
the strangler pa,rtly or íully closed, a deposit oí
cartx)n will be íormed on the cylinder head and
piston crown, and in the ports, which will be soft
or sooty in texture. If, on the other haind, tho
Íormation of carbon is due to over-oiling (;.c to
running too rich a petroil mixture, see pa.ge 34),
then the deposit will be much harder and more
difficult to remove.
A study of the carbon deposit will provide a
useíul indication as to its cause, particulaïly ií it
is excessive in qua,ntity. The main symptoms
indica.ting an excessive a,mount of carbon deposit
are an apI)reciable decline in power, a tendency íor
the engine to be rough and overheat, and íor it to
run erratically, particularly at low throttle open-
ings. \men a stage has been reached at which
thffie symptoms are evident, decarbonisation is
clearly overdue, aI`d the wise owner oí a small
two-stroke such a.s the B.S.A. WINGED WHEEL
wiu find that it pays to work to a definite schedulo
oí decaJbonisa.tion on a mileage basis, instea.d oÍ
wa,itilig íor the erigine to show signs oí digtress
beíore mdertaking this work. For this purposo
Table ll. is given a.s a useíul guide.
24
(
TABLE II.
RECOMMENDED DECARBONISATION
PERIODS.
nem. Decarborise every
Exhaust Port ... ... l,OOO - 1.2OO miles.
Siloncer ... ,.. Exa,mine at saimo
time as exhaust
port, and decapbon.
ise ií necessary.
Cylinder Hea,d md Piston 2,000 - 2.400 miles.
Exhaust Port.
Accumulated carbon in the exha.ust port (;.é, in
the cylinder aperture). and also ili the first inch or
two of the pipe, is the most prolific cause oí power
loss, because it has the effect oí reducing the alm
oí tho orifice through which the exhaust gas ha.s to
pass on its way out of tho cylinder, a.nd it thereíore
ofrers increased ba.ck pressure.
Fig. 10. View into port with pipe off and silencer
disma,ntled.
2.5
' i ï ! ͧí í í