engine chuggin

Whether or not you agree with the carb application here, it should be irrelevant as too this issue. If it's occuring at light to 1/4 throttle, he won't be into the secondaries anyway. Minor jetting differences aside, it will act like any 600, (DP or Vac) on the primaries. As to the intake, is it the dual plane or single plane?

I'm sticking to my post #7, timing first!

I am however, curious if when you tuned as best you could out of the box, that you checked/set the float levels?

Just to explain my overadvanced theory from earlier, here's a senario.........Initial is at 20*+ and a vac can pulling in a lg. number hooked to ported vac....... It starts and idle's ok, but as you start to accelerate your bringing in the vac adv so now your approaching 40*. As the rpm's increase, the mech adv is growing and now your close to 60* and the engine just isn't liking it........just 1 of many possibilities.