My '74 2.0L w/dual Weber 40s, Pertronix II electronic ignition, SS heat exchangers and Triad dual outlet exhaust back fires when I let off the gas (usualy around the 2.5K RPM range).

The car runs great, idles low and smooth and has plenty of power in all ranges.

I hear a loud pop and fast bap, bap, bap, bap ....when I let off the gas (2nd or 3rd gear around 2.2 -2.8K RPM).

Is it my type of exaust (Triad dual outlet, large diameter pipes "track style"??).

Exhaust leak?

Timing?

What is the correct torque value for the SS HE to head? SSHE to exhaust?

I know I need to get under the car (maybe this afternoon) but what to do suggest to look at first.

Thanks !!!

I'd look for exhaust leaks first. Be careful when tighting on those ex studs that you don't snap them off.

Sometimes you can can actually see or feel the ex gases leaking at the head/heater box connections.

It can also be due to one or more of your carb barrels being lean (check for plugged idle jets/float adjustment) and can also be due to one or more of your carb barrels being too rich. I've had both occur. Good times! The instance where I had similar symptoms as you was when I was running pretty lean. Exhaust leaks are a very good start though.

-Chris

First check the muffler to HE connection. Those gaskets are one-use only. The stuff inside crushes when the bolts are torqued down. My EXACTLY similar backfire came from a leak there.

I have had similiar issues in the past with my Dells - otherwise ran great. finally solved by going one step smaller on the idle jets.

My vote: Too Rich

It's an air cooled Porsche. End of story.
Mark D.