engine chuggin

Well, first off, while you can use a little more initial timing then 10* BTDC, it still shouldn't be bucking/chugging with the timing you have now. One other thought is, i looked up the power valve that comes in the 600DP and it doesn't open until 6.5" of vacuum. Considering a stock 318, you're probably making 18-20" of vacuum at idle and cruise rpm and you may be going lean at part throttle because of that. It would take quite a bit of throttle opening to drop the vacuum that far and that's the reason i asked about wide open throttle. A 10.5" valve would probably be more appropriate? By the way, the stock jetting should be a #66 jet which should be fine for your application with that carb....Just a few of my thoughts.