Thanks for the reply gentlemen. Hey Longhorn, I think you may have hit it on the head. After reading your reply, I starting looking up accelerator pumps on the internet and there are a couple YouTube videos made by Holley specifically regarding this issue (my carb is a brand new Holley 670 Street Avenger that was installed with my new crate 350/290 in October). The sound I was trying to describe sounds exactly like the sound of the pop when the carb backfired and chokeplate snapping closed. When it first happened, I thought it was the TV cable ratching loose, like if the cable was binding and too tight and popped. She is just about due for the 500 mile oil change, so I am going to have this issue checked along with the timing. One last question, could the timing be off due to the vacuum advance being hooked up? Chevy recommends that with this engine and HEI distributor I also put on brand new with the engine, carb and wires that the vacuum advance is supposed to be left disconnected and the engine is designed to operate using only the centrifugal advance to achieve the correct timing. My mechanic hooked up the vacuum advance about a month or so ago, which gave me better acceleration in first gear, but that is also when this new issue started.
