Vacuum advance problem ?

I just hooked my vacuum advance up. Had to put a fitting in the intake to hook it up as there was no fitting in the 750 holley that is on there now. Took it for a test drive and the engine seemed to be hitching as you go along, running quite rough. I unhooked it and everything was ok again. I had already set the initial timing first, with vacuum line plugged off. Have no light so just adjusted it until I had only a very,very slight ping at WOT. Could the vacuum advance have brought the timing ahead too far to cause this roughness or hitching as you drive? When I hooked up the advance the rpm only came up a very slight amount. Should I try to adjust the vacuum advance diaphram? The previous owner never had the advance hooked up, but he raced the car some, and I guess a lot of people don't use advance when they race. I drive on the street quite frequently so I was hoping the advance would give me a slight fuel mileage increase and it should be a little better around town driveability wise. Also could the distributor have been reworked in some way to cause this. I'm not sure what to look for. Thanks guys. Keith
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