Have a 68 Camaro with a '78 Vette 350SB Motor(don't know the compression) as the motor was done by a previous owner. Running a GM HEI distributor with an ACCEL Coil along with a MSD 6200 Ignition. My question or problem is that I just switched out the carb today to a Edlebrock 1405 to match the manifold. The vacuum advance on the old Holley was capped along with the vacuum advance on the distributor. Determined that the carb has a full vacuum present at idle. However, when I hook a hose from the vacuum advance on the new or old carb to the distributor the car backfires and boogs down. My question is why would the car be set up like this? Wouldn't I be losing any power by not having it hooked up? The Car runs fine with the new carb set up but still have a slight detonation at the higher end of the power band or under load(for instance under acceleration in 3rd or 4th gear).