[Everett#2390]

A blown power valve will give a bad running engine at idle, lots of black smoke from the exhaust due to rich fuel. However, doesn't mean its bad, a check of the valve itself would be the order of the day, I think.

A bog is usually caused by not enough initial timing, idle mixture screws too lean, a vacuum leak, too small of squirter size on primary side, or secondaries opening too soon.

 

[Everett#2390]

If this engine is a 68 and older SBC, then the balancer timing mark will be coplanar with #1 cylinder, i.e., point in the same direction, but parallel to #1 cylinder centerline.

This is where a metal coat hangar comes in handy, a pointer for TDC.

I myself use a vacuum gauge for timing and tune for max. Then, I back off at 2* increments until the hot engine starts without starter kickback from over-advanced ignition timing, and there is also no pinging at WOT.

You're welcome.