ok boys heres the deal, my sbc 400 was running minty after being tuned at the propane shop only at 8deg adv as well so it was running good. But today after running her fro about 3 hrs in the bush she started to knock! now its not rod knock its a misfire comming from my ignition now when i disconnect my vaccum adv it goes away. But when i put it back on it knocks again is my HEI screwed or what cause im running out of ideas haha . It was also backfiring and stuff when i put load on it almost like the timing was out. But it cant just jump timing cause it idles perfect. Only when i put load on it with the vaccum adv hooked up will it knock like CRAZY!!!!