Generic Onyx 50, Service Manual

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Remove the spark plug; check the
colors of spark plug insulators
and judge the proportion of
mixed combustible gas based on
abnormity
The spark plug insulators are black;
the exhaust muffler emits black
smoke or causes backfire if the
engine works at low speed; bad
acceleration property; instable idle
speed; flameout probability; it
works normally at high speed.
The spark plug insulators are brown
The spark plug insulators are
white; the engine may intermit
during acceleration; the
carburetor generates backfire;
insufficient power of engine
Mixed combustible gas
is too dense.
1. Check whether the air filter is
blocked.
2. Check whether the startup device
for carburetor (startup & enrichment
system) works normally.
3. Check whether the float needle
valve is too low.
Normal combustible gas mixture
Check whether the cylinder
outlet or the exhaust muffler
is blocked due to accumulated
carbon fouling.
Check the
lubrication system Mixed combustible
gas is diluted.
1. Check whether fuel
cock works
normally.
2. Check whether the
float needle valve is
too high.
3. Check whether the
measuring jets and
drill ways in the
carburetor are
blocked.