Backfire?

[Edward Rognerud]

During the last 2 flights in our PA39, after flight while taxiing back to hangar, the right engine made a popping sound 2 to 3 times while at idle power. It sounded like a mild backfire. It has never happened before since we have had the aircraft. We just had both fuel selectors rebuilt. These were the first 2 flights since that work was done. Any ideas what may be causing this?

Ed Rognerud
Rosemount MN

[Kristin Winter]

First thing to do is check the idle mixture setting. Take it up around the patch enough to get full operating temp. Then with the engine at idle, and the boost pumps on (per Piper SM), bring the mixture back. You should see a slight drop in MAP and a slight rise in rpm just before the engine quits. If you don't, adjust idle mixture wheel on the fuel servo and try again.

[Edward Rognerud]

Thanks Kristin,

I will try that and see what happens

Ed