I just got my new motor running and it runs fine when I have the idle up around 1100-1200 but when I back it down it starts to surge up and down. Ive set my initial timing at 16, and have tried 10 and then 20 and it still does it when i back the idle down. Engine runs awsome when I gun it, no stuble at all. Does this sound like a vacuume problem? or a carb problem? I've read that If I dont have my secondaries set right that minght cause my problem. Any Ideas?

Heres my specs
402 .060 over
crane 272h10 cam .515 .515
Speed demon 750 Vac secondaries
Accell HEI
9.5-1 comp.
dynomax 1 3/4 headers

oops, this probably should have gone in the engine section, sorry. Any help will still be appreciated
Steve

anyone?