No-load Misfire Puzzle
go with a smaller primary rod.jmo
surge at cruise=lean
fine at wot=main jet seems within or close to good, but check spark plugs color.
what/how much total timing are you running cause the other side would be that you have too much vac advance timing or mech timing and my need to tune it out some take 4* out of it by means of a lil allen wrench into the vac canister nipple or turn the distributor clock wise to retard it 2*-4*