1990 Johnson 140 Mystery

[Pallet]

Engine runs perfect 80% of the time. The other 20% it is more difficult to start, but runs fairly smooth. During this poor running (20% time) engine will not go much past 2000 rpm's. Throttle can be pushed fully and engine will not bog. Occasionally when running like this, something will move, clear, ? and engine will accelerate normally and run fine for rest of day. Fuel filters and spark plugs are new. When placing in reverse during this time, engine will rev over 2000 rpm and will also occasionally accerate normally after doing this.

Any ideas?

Thanks, John

 

[HighTrim]

Re: 1990 Johnson 140 Mystery

Its not overheating at all is it?? Have you started with a spark and compression test? Use a temperature probe and verify that the engine is not overheating. Disconnect the tan temperature wire from the pack and retest. If the engine now performs properly, replace the temperature switch. Make sure the tan temperature switch wire is not located next to a spark plug wire.

 

[ezeke]

Re: 1990 Johnson 140 Mystery

And remember that your motor has both QuikStart and S.L.O.W.

That means that the powerpack has a black and white wire from the temperature switch on the port cylinder head. That wire sends the signals that the engine has overheated and to slow down, or that the engine is cold and that the timing needs to be advanced for a cold start.

BTW, The temperature switches almost never go bad, so check everything else first.

 

[levittownnick]

Re: 1990 Johnson 140 Mystery

I think it is the Shifter Switch or it's mechanism hanging up. This switch is supposed to momentarially kill the port cyllinder bank while shifting. It is just supposed to do that for a split second but if it hangs up, the port bank is dead--- NO Spark. On my rig, if I shift it to reverse and then foward, it will clear.

Good luck.

 

[ezeke]

Re: 1990 Johnson 140 Mystery

Shift assist was not stock on the 140, so if it is installed, it was by you or another owner.

 

[Pallet]

Re: 1990 Johnson 140 Mystery

Thanks, I will check these items. The engine is not overheating and compression was good.

 

[clemsonfor]

Re: 1990 Johnson 140 Mystery

are all carbs clean and not plugged up, this would not explain the reverse thing unless its just coincidence!