Douglas Gaither wrote:
> I am currently driving my father's '73B. It was not quite warming up so
> I installed a 195 degree thermostat. Everything was cozy. After about
> a week, I started experiencing backfires. It occurs after the engine is
> warmed up and under moderate throttle between 2500 and 3000 RPM. I did
> some research on the list archives and found several comments that
> backfires are caused by too lean of a fuel mixture. I noticed that the
> rear carb damper continually loosens due to vibrations. Thinking this
> could be the culprit, I filled it up with oil and tightened. After the
> engine warmed up again, backfires again occur. I pull over and check
> the dampers and it is fine, but it looks though the radiator was seeping
> a bit. I also noticed that the backfires totally toasted the foam air
> cleaners!
>
> Could my installation of the high temp thermostat caused my backfire
> problems?
> What would you suggest for me to try to remedy this problem?
>
> I know I could just try purchasing a lower temp thermostat and see what
> happens, but I wanted to consult the list first.
There are two main sorts of backfires, caused by lean mix and rich
mix. In general, the lean mix backfire occurs when the throttle is
opened rapidly and the backfire is out the carburetor, like yours. The
rich mix backfire usually happens on over-run and comes out the
exhaust. Since you are toasting the aircleaners, yours sounds like a
lean mix backfire. A hotter thermostat would warm the engine up
faster, and if you have the water-heated intake manifold, that would
heat up faster too. A cold intake manifold causes fuel condensation,
resulting in a leaner mix, so the hotter manifold should not be
causing your problem.
I would check for air leaks in the intake system or a malfunctioning
choke assembly.
-Rock http://www.rocky-frisco.com
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