Popping on decel, fuel pressure regulator? Options

[PDXMike]

Hey all,

My 75 1.8 L-jet has always popped on decel. I've looked for exhaust leaks, including dropping and reinstalling the entire exhaust and getting it smoke tested. My decel valve is working correctly. This thing makes a LOT of noise, even when just letting the engine spin down with the clutch in. It sounds like some crazy-tuned dirt track stock car or something. This is fun for the first 5 minutes or so, then anybody within 100 yards of me wants to run me off the road.

While testing my decel valve, I noticed that the same vacuum line that controls the decel valve also runs to the fuel pressure regulator. Is it supposed to cut the fuel supply off when vacuum pressure goes up? Could this have anything to do with my popping? If the injectors are still firing I'd be pumping gas right through into the exhaust, right?

I have a Monza muffler, which probably isn't helping.

Is this a crazy theory? What else can I try?

Thanks,

Mike