[Eric Schaeffer]

I have been experiencing fairly aggressive backfiring upon decelration. Car is fine at idle and under acceleration.

I assumed that it was either or a combination of too rich a mixture and/or an exhaust problem. My unscientific tests of putting my foot over the exhaust and the car gasping for air but not stalling and looking at how black the exhaust smoke was seemed to confirm it is a little of both.

Then someone casually suggested that it could also be a bad selenoid (part #51 from the Early Porsche 911 Fuel Injection exploded diagram).

I disconnected this part and......no backfires. It stalls at idle sometimes but no backfires.

What does this selenoid do? Why would it fix the problem? Is this a viable long term fix or should I replace it?

(I will address the rich mixture and exhaust problem but I am trying to understand what/how this "fix" "solved" if anything)

It's a '70 engine with Zenith carbs.

Thanks
Eric