thunderbolt ignition on a 500 50 hp

[bubblegump]

why would this engine which has a distributor fire on 1 and 4 and doesn't seem to fire on 2 and 3? when I pull the plug wires off on no 2 or no 3 it doesn't seem to make any difference. also it will not rev above about 1/4 throttle

 

[RCO]

What is the serial number? Some model 500's had a Fairbanks Morse magneto that looks like a distributor, later ones had a distributor with two driver coils with an external coil.

 

[bubblegump]

3822545