1978 70 Hp Johnson Missing Problem

[jay_merrill]

Re: 1978 70 Hp Johnson Missing Problem

I wouldn't think that junk in the carb would make it run rich, but it certainly could cause missing. I became focused on ignition because of the tendency for the motor to miss after it ran warm for awhile. This is something that is common in CD ignition systems. I would go ahead and run the motor again, but try to duplicate what you were doing before, just to see what it does.

BTW, does your motor have the warm up function on the choke solenoid ... is there a temp sensor on the port side of the head, which goes to the 12 VDC electrical distribution block? If so, there is a service bulletin that recommends disconnecting it, because the half actuation of the choke that it causes, tends to foul plugs. It actually should foul all three if it is doing that at all, but its just a thought.

 

[ezeke]

Re: 1978 70 Hp Johnson Missing Problem

Glad that worked out for you, karlp.


BTW, The automatic choke solenoid problem that was addressed by service bulletin #1335 in February 1974 was for an earlier series of motors. The motors affected by SB 1335 have 2 positive wires running to the choke solenoid; one is purple with a white tracer and the other is purple with a yellow tracer. The 1977 and 1978 70HP and 75HP motors did not have the feature or the wiring for it.

 

[jay_merrill]

Re: 1978 70 Hp Johnson Missing Problem

Glad that worked out for you, karlp.


BTW, The automatic choke solenoid problem that was addressed by service bulletin #1335 in February 1974 was for an earlier series of motors. The motors affected by SB 1335 have 2 positive wires running to the choke solenoid; one is purple with a white tracer and the other is purple with a yellow tracer. The 1977 and 1978 70HP and 75HP motors did not have the feature or the wiring for it.

I was under that impression too, Ezeke, but you never know what powerheads you are going to run into on someone's motor. I don't even know if one of the earlier powerheads will bolt up to a 1978 midsection, but they might. To me, the old OMCs are like old Volkswagons - you see all sorts of "mix n match" combinations!

 

[ezeke]

Re: 1978 70 Hp Johnson Missing Problem

I wouldn't think that junk in the carb would make it run rich, but it certainly could cause missing............

What causes the individual cylinder to run rich is a sinking float or bad float needle that allows fuel to keep entering the carburetor because the float valve is not stopping the flow as it should.