Gary Buster wrote:

Here's one you can help me to be a better neighbor...

I have not ever been able to silence the beast when I shut down the engine after
running hard or idling on the tarmac to "cool down" after flying...  she still lets
out a distictive BAM when I shut it off.  (just seconds after I kill the switch!)
The Inconel header has muffled it, but it is still VERY present.

Someone out there knows how to calm this down or possibly even eliminate the
backfire... I am scaring little kids at the airport!!!

Help!!

Gary Buster
N263GB Tandem Gyro ported 12a

Gary what is your induction system like? As I recall it is a Weber carb
on a long manifold. I would guess a backfire is caused by an explosive
mixture in the muffler. Aircraft engines are shut down by leaning them out.

Sounds like your mixture is way too rich at idle or low power. Just a guess 
I could be out in left field here. Webers take a degree in the Italian school
of carburetor design to get right over the RPM and power range. Aren't 
there about three or four sets of carb jets to change? Seems like an O2 
sensor in the exhaust pipe with one of Ed Anderson's instrument panel LED's 
might be what you need to set the mixture at low power and idle. Page out 
of the EFI book. Oh if we only had something like that back in 1965 when
we were all running Webers in our racing cars.

Paul Lamar
 
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