Vapor Lock

['68OrangeSunshine]

The set-up is a 350 crate motor: (about 25,000 new) SM465, Carter AFB 600cfm, Weiand 8004 intake, Heddman Hedders, Mechanical fuel pump -- [Stock AC Delco]. Fuel comes from stock blazer tank in frame aft of differential. HEI ignition. [Cannibalized unit from my previous ride, a '67 Sub K/10 w/454.] Replaced all distributor components about 3 years ago. Maybe module's gone bad. It's a cheap enough fix.Had a similar problem 2 years ago when hedders were burning up plug wires (ignition would cut out when under load and hot), went to white fiberglas braid wraps around plug terminals and hi-temp silicon wires. Same jacketing is on fuel line coming up from pump to inline gas filter [G15]. Fuel line runs about 1 1/2" from block.
My buddy rode shotgun with me today when we went to get my 292 block back from machine shop. I thought I heard the pre-burble and got his attention. He said he thought he heard a "whistling" from engine bay. Manifold, headers, collecters? Could be there -- I wouldn't hear it after 4 years around high pitched jets in my misguided youth.Could burned out header or collecter gaskets contribute to this effect?