Backfire 71 440 .

[6 pack]

1971 Challenger 440 sixpack ,have been having backfire when shutting the car off in park.It does not backfire if I shut the car off in drive,with my foot on the brake.Is this mostly a timing issue?

 

[Bret Schneider]

Sounds like the idle speed is too high. Putting the car in drive with the brake applied is lowing the idle speed enough to alleviate the backfiring.
Does the engine use some sort of idle speed solenoid or dashpot? If so, maybe a problem there.
And yes, excessive base timing can also lead to a high idle speed. Another common culprit is a vacuum leak.

 

[6 pack]

Yes it does have a idle speed solenoid.Was thinking about removing it.Thank you.

 

[Chryco Psycho]

Probbaly idle RPM , you can lower the idle speed a bit

 

[Bret Schneider]

"Yes it does have a idle speed solenoid. Was thinking about removing it."

I wouldn't be so quick to remove it since it's job is to address the problem you're having.
Rather check to see if it's working. The plunger should extend out when the engine is running. Idle speed needs to be adjusted at this time. Turn off the engine and the plunger should retract closing the throttle plates to minimize a run on condition.

 

[Challenger RTA]

Think simple! I just had an issue. Started my car a few days ago and it was running a little ruff. As you mentioned a back fire or two I had. Removed distributor cap and found a bit of corrosion cleaned it up and fix the problem. I did replace both rotor ,cap and checked plugs and wires a day or two later. Before I did that it was running a bit rich. It fixed that problem too. The point being, make sure all the components are in good working order. Tune up.