Small glitch

[henryban]

I have a 1998 135hp Johnson O/B. It starts and runs perfectly except for one minor glitch that has turned up in the last few months. If the motor sits for more than a day or so during the first ten minutes of running at 1200 to 1400 rpm it seems to skip for an instant and drop about a hundred rpm. It is most noticeable if it has been damp out. After the ten minutes or so the motor idles, and stops and starts just fine.

About six months ago, or about four months prior to the skipping I disengaged the automatic oil and went to a manual oil mix.

I doubt if it is a plug problem but I am going to change them out anyway.

After that what do you think would most likely be the problem?

After thought... It is an up tick in rpm, like a plug is kicking in every few seconds.

[boats.net]

Might check the wire connections at coils for corrosion, check all ground wire connections are making good contact. Inspect plug wires and boots for damage and connections.

[henryban]

It was probably a bad ground.

For some troubling reason involving my faulty brain every electrical glitch that I tackle seems to always come down to a bad ground.

I still have to wait for a damp day to see if my fix will work but I am very optimistic. It idles smooth as silk for now.

I started switching and changing plugs; that did not seem to do it. Then I did the same with the plug wires; ditto. The last thing I did was to pull all four coils and clean up the ground contacts; I think that’s what may have done it.