Hi, looking for suggestions, I have just removed the Mallory dual point distributor from my 350 and replaced it with an original single point model. Reason for this is that the Mallory had no vacuum advance and I figured after reading up on the forum that for street use the motor would perform better with vacuum advance (which it does). An issue though, sometimes when I step on the gas after coasting the motor will give a single cough and then start to pull normally, this problem diminished a lot when I changed out the two heavy springs that came with the distributor for a light and medium spring, the advance is now all in around 2500 RPM and approx 35 deg BTDC with the vac disconnected and plugged. The motor winds over easily enough and there is no sign of detonation. Idle mixture is set at highest vac which was 17 In Hg.
Under deceleration vacuum can go as high as 25 Hg which can pull oil past the piston rings and thru the intake valve guide. I don't know the condition of your engine but if it has a lot of miles the high vacuum could be coating the plugs with some oil which could cause a momentary missing condition. When running a vacuum advance shoot for 50-52 degrees total advance at cruising speeds. And then don't exceed 38 degrees mechanical advance. Remember, the vacuum advance doesn't work at all under full power and is there just for better fuel mileage.