29 dodge fordor, 360-727, been on the road a few years, some time ago, changed carbs, hooked up distributor vacuum line and it ran like shit. 2 bbl carb, reversed lines to full vacuum at idle, worse yet, unhooked vacuum line, set timing, runs like a clock. This winter, a lifter let go, so, new cam, lifters, all stock specs, set timing, runs like a clock, hook up vacuum advance, runs terrible, stumbling, backfiring, but only if you crack the throttle hard. If you bring the rpm's up slowly, runs fine but has a poor idle. Advance or retard distributor, makes no difference. Switch the line to manifold vacuum, runs like crap, ported vacuum, idles fine but won't run smoothly at anything above idle. Advance or retard distributor, no difference. Unhook vacuum line, runs like a clock at all times. Timing chain new, everything checked twice or three times. 1974 360, donor was a one ton motor home originally.