What's the total timing advance with the engine running at cruise speed, and the vacuum disconnected? It should be 37 degrees or less, increasing to about 45 degrees when you connect the vacuum. On a pull, the vacuum goes away, and you're left with centrifugal advance only. Just a few degrees of over-advance will cause the symptoms you're describing, trying to run the engine backwards at full advance. I do a distributor recurve on some applications, actually reducing the centrifugal advance and making up the difference with the initial advance. This gives better acceleration without getting too much timing at cruise speed. A too-lean carburetor in the midrange and/or cruise range can also cause surging at light throttle.

Check your PCV valve vacuum line to see if it's pulling oil through the line and burning it. If the inside of the vacuum line is wet with oil, it's the source of the smoke. Some aftermarket valve covers don't have enough baffle built into them to prevent oil from entering the vent system.
Jerry

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