I think popping on trailing throttle is caused by a
combination of things. The ignition advance is
regulated with vacume which is much higher during
trailing throttle. Your spark plugs fire at the wrong
time. The carbs are shut when your foot is off the
pedal. The engine is still turning high RPM's. This
causes the wrong mix of air/gas. I can't remember but I
think it becomes way too lean. Engine braking also
causes blow-by at the rings. It can make your oil get
dirty faster. On a side note, this is one of the
reasons new cars have fuel injection. When you take
your foot off the gas, the injectors stop injecting.
This is not as much for engine protection but for
environmental reasons. A high percentage of emmissions
are caused by trailing throttle on carborated cars. A
very small percentage is caused during acceleration and
steady cruising. In fact almost all auto emmissions are
caused during startup and trailing throttle. They fixed
the trailing throttle problem with fuel injection. Now
they are concentrating on startup. Some new cars have
fancy converters and exhaust air bags. Another side
note, motorcycles have much higher emmissions with much
smaller motors. They are just now starting to build
them with fuel injection.
If you want a really big boom then switch the ignition
off while on trailing throttle, (just for a couple of
seconds) and then back on. Make sure to circle back
around to pick up your muffler.
NT
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