I noticed that my 73, 2.0 with original FI and points, has begun "popping" when I downshift. The popping noise appears to be coming from the exhaust. This usually happens only when I aggressively downshift. I figured I would adjust the valves and that should take care of it. Just checked them and only had to adjust a few slightly

Now what? Is this a timing/dwell issue?


Warrenoliver

10 out of 9 causes for exhaust pops on overrun are leaks in the exhaust. a pinhole will do it. feel around *CAREFULLY* for pulses and possibly have a look under the car in the dark - sometimes you get quite the little lightning show of fire through the pinholes.

Unless it really obvious...leaks are a bitch to find. Leaks are usually at weld spots and bolt connections.

I have had luck by taking a cold bucket of water and sticking my hand it.....waving wet hand under the motor and finding a breeze when reving motor. This and any other method requires either L O N G arms or a helper......

You can also mix up a bottle of Dawn and water.....spray it on and look for bubbles....hot surfaces aren't the best with this method though....Dawn and water are best for cooler piping under pressure.

with exhaust leak, which can be hard to find. Check the muffler, all exhaust gaskets (muffler and cyl head), and heat exchangers. Wipe around all the flanges and see if you can find soot, an old white t shirt works good for this.

As a last resort you can turn the mixture way too rich,run it and make it pop several times, and see if you can then find soot. Be careful though as you want to make sure that you get the mixture adjustment back to where it should be, and you can also foul your spark plugs.

Also check your intake manifolds and gaskets. I know yours is injected, but on mine (carbed) if there is an intake leak, I get pops just like that.

BTW: I am heading up north tomorrow night. A few weeks in the woods will do me good.

Popping?

Could be...

Intake leaks (too lean exhaust)
Valve guides
Valve adjustment
Exhaust leaks
Timing