Hi, I have a 140 johson not sure of exact year but was told mid 80`s ,nothing matches on motor, the lower half is a 1981 according to the numbers on the transom bracket white in color and info from the po the power head is approx.1984-1986 black in color according to the po who said he rebuilt it but had to use that block because the original block had too much damage , anyway my problem is that when first starting it start right up but run`s poorly after a few minutes (2min approx) it smoothes right out and runs well no problem starting or restarting.. compression is 118-120 in all cyl. fuel is new ,carbs are spotless wires are new as plugs are also..I have not tried it in the water yet weather was to windy, but running it on the muffs I pulled the plugs after running and noticed cyl 1 and cyl 2 were a little darker than 3&4 .. All cyl are fireing pulled off wire while running and can hear and feel the difference..and temperture is cool have guage and warning buzzer all good,
not sure where or what is causeing this any ideas or suggestions would be appreciated Thanks in adsvance Bill
not sure where or what is causeing this any ideas or suggestions would be appreciated Thanks in adsvance Bill 
