THE VeloSoleX S
can be significantly improved by tuning its engine.
Before tuning make sure that the bicycle is fully
serviced and running well. This means checking
that the Tyres are in good condition and pumped to the
correct pressure, the Brakes working correctly, the
Engine decoked if necessary, the Exhaust Silencer replaced
if old, the Spark Plug in perfect condition and gapped
correctly, the Engine and Head Gaskets replaced if necessary,
all Nuts & Bolts tightened to the correct torque,
the Carburettor clean inside and out, the Contact Breaker
and Condenser in perfect condition, the Ignition Timing
adjusted correctly and the Fuel Tank Filter, Carburettor
Fuel Filter and Carburettor Air Filter replaced if necessary.
With regard to Engine Ports, "Two-Stroke
Tuner's Handbook" by Gordon Jennings (1973) correctly
that mistakes can EASILY
be made while tuning, but are COSTLY
to rectify! A lot of the data in the Gordon Jennings book
was derived from empirical research on 2-Stroke engines
with the recommended TIME AREAS based on Scatter Plot
Data trend-lines measured on a large number of 2-Stroke
engines - the VeloSoleX S
being one of them!
Also some points need to be
clearly understood BEFORE attempting
to modifying any ports:
When using the VeloSoleX S
3800 on long downhill runs, do not keep the throttle closed
all the time but open it every now and then.
Otherwise the engine will have a lack of lubrication,
overheat and run slowly or even seize completely.
- It must be remembered that the VeloSoleX S
3800 is a
and that the Engine was not designed to exceed 4000
- The VeloSoleX S
has small ports which are not easy to
map onto graph paper in the standard way and some Rules
Of Thumb are required. Even if the
theory suggests that the
TIME AREA or ANGLE AREA
requires changing by filing away material there is little metal available around the port
in the cylinder to do much with.
- The VeloSoleX S
is Piston-Ported which means that the piston
is used to open and close the port holes. Although
simple, this does result in undesirable SYMMETRICAL port timing either side of TDC (Top Dead
Centre), normally resolved by fitting a One-Way
Reed Valve in the Inlet Port. Unfortunately,
there is not enough room in the Inlet Port to fit a
Reed Valve, so other port improvement
techniques must be found.
- Port Height changes of 1 mm can result
in SIGNIFICANT changes
to engine performance.
- Port changes
are INTER-DEPENDENT on others.