vacumn ?

Ok I am running a 318 mild port heads, headers, eldebrock ol torker single plane intake with 600 cfm eddy carb.
When I put foot in it vac on performance gauge goes to 0 and get misfire at 3500 to top end.
Timing set at 13 btdc
When I keep performance gauge at 4 to 5 and accelerate slow no missing happening.
Is this a issue with the secondaries ?:banghead: