Bill,
Backfiring can mean a couple of things. In the owner's handbook,
(English english) it means "banging in the silencer". That is when
unburned gas/air from the cylinders gets through the engine and into the
exhaust, and then it lights off with a bang. Think of driving along in
an old Chevvie, turning off the ignition for a second, then flicking it
back on. This gives a very satisfactory bang, some smoke, and can be
done several times before you need to drive to Midas for a new muffler.
Mechanical causes of this can be faulty or sticking exhaust valve, rocker
clearance too small, or a mixture that is much too rich or too lean.
When coasting with throttle closed, can also be that the throttle is not
completely closed.
In the English english context, there is also "spitting back in the
carburettor" , a term we tend to include in backfiring, though it's not
the same thing. This is usually caused by weak mixture, or air leaks in
the suction side, and can be caused by too tight clearances of intake
valves or sticking guides.
Bob
On Sat, 08 Apr 2000 09:57:50 -0400 Bill Saidel <saidel@crab.rutgers.edu>
writes:
> Here's another ignorant (albeint not unlearnable) tuning-beginner's
> question:
> What does backfire mean?
>
> The details are
> Not under load, the car in neutral runs up to 4000-4500 purringly.
> But take it out on the road and it backfires at 2,3,4000. So I
> haven't gone
> very far yet.
>
> Could someone send me a simple lesson on the meaning of backfire?
> TIA,
> Bill,
> 76B with the 73 carbs
>
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