1981 Johnson 150 hp missing @ idle

[jbinjc]

I have read a lot of posts still not right.
Hi all just got boat out of storage and real bad miss. Changed plugs & wires, fired right up miss progressively gets worse from initial start. Checked plugs & soaked with fuel & oil. Pulled wires 1 @ a time to determine if dead cylinder. Middle 2 seem to not have near as much spark as top 2 or bottom 2. Plugs in worse condition on those 2 cylinders. Please help w/ ideas. I am pretty sure it is not bad gas just can't determine if over fueling or power pack problem.

 

[emdsapmgr]

Re: 1981 Johnson 150 hp missing @ idle

Put an inductive timing light on each plug wire and compare the flashes between all 6 wires. The timing light will show misfires, weak firing and no fires. You need to determine if your miss problem is spark related. You indicated that your testing shows the two middle spark plugs have weak fire. Your unit has two power packs, each of which provided spark to one bank of cylinders. You can swap them for testing purposes. It is unusual for both of the middle plugs to misfire, indicating that the packs may not be the main problem. The 6 coils usually have low failure rates, but you can swap them around to see of it makes any difference. The last two major ignition components are the stator and the timer base, both of which need to be diagnosed according to the factory service manual. They are expensive and worth spending some diagnostic time on prior to purchase. You can get an original factory manual from Ken Cook Co., in Milwaukee.