hi Jim , ,

sounds like a misfire due to two plugs firing at closer/farther intervals.


Check the vacuum- and centrifugal advance mechanisms in the distributor - if either of these are seized, thenthe timing will look fine at idle, but it won't be advancing correctly as the engine speed increases. The result
is an engine that feels sluggish, together with significantly increased fuel consumption...

after a check of your sp wires, for cracks, damage worn heat damage proper hookup, , check the timing, even valve check might help - especially on cyl 2 and 3 - is there increased smoke at various times (idle, accel, decel. etc)

good luck

ozzi
67 220s