my car runs great!, except... Options

[lotus_65]

...for the most insane backfire known to man!
('74, 1.8, dual 40's, stock ignition, 2l sshe's, bursch, 3lbs fuel pressure, compression: 1-25, 2-26, 3-55, 4-65 but they hold those numbers)

i finally have the carbs dialed & running good. (some people know this engine and it's car sat for years [decades] under a willow tree on a farm). fresh valve adjustment done last weekend.

last night i was running it and modulating the throttle from 1/4 open to 3/4 open to try and draw out a backfire (this has been happening on decel) but i couldn't get it to explode, so i thought my last adjustment was good.

i had been running somewhat rich, so last night's run was to try and lean it out as much as possible. i got home and shut the car off and i thought i was going to find the muffler it pieces after what sounded to me like a frickin' cannon shot about 5 seconds after shut down.

i've already decided i'm taking it easy on this engine, but i need to resolve this. and i'd rather not have the neighbors think i'm firing shotguns in the garage.

paul