VintageOutboardMan, if your ignition is in order, then it should fire off easily with premix shot in the cylinders, even with 60psi of pressure.
I would invest in a $6.00 open air spark gap checker. If, it can easily jump 1/4 inch with a nice fat blue spark then your magnets, coils, condenser, and points should be in good shape.
The other component of the ignition is the timing. Things that could effect your timing despite setting the points to 0.02 inches or using a timing fixture. These specific issues will affect timing of the spark. Optimal timing is when spark is produced at the top of the piston stroke igniting the compressed fuel mix/air charge. If spark is produced at other times then there may not combustion or back fire.
– crossed ignition wires. (top on the bottom and bottom on the top spark plugs)
– breaker cam that is up side down. (make sure the word top is facing up)
– movement of the breaker cam (due to damaged cam or key)
– damage key or flywheel key way mating.
– ignition plate slop and movement
