ISO Johnson Mechanic!

[Shopguy]

I working on a toon for a guy and it has a 2005 Johnson 115 v4 on it. Problem is very consistent and repeatable. When you ease the throttle up off idle it begins to shudder until it hits 1600 rpm. Above that it purrs like a kitten. Ease it back down and it begins to shudder again under 16-1700 rpm. A little hard to tell on the hose but since I had it on the water once, I can hear it doing it. In the water under load it's very noticeable. Idles good and runs out good just has this annoying shudder like it's dropping cylinders below 1600rpm.

Compression is 145 on all cylinders
fuel filters clean.
Correct plugs installed and gapped to .030
Added Mercruiser Kwik Clean fuel additive to tank.

Leaning towards an ignition or computer fault, both beyond me without a laptop and software.

Anybody got any ideas?

[lakerunner]

Anchor works for me on those crap johnsons. I have good luck on old OMC motors talking to Ray Ward on qualls road

[BobG]

Leaning towards an ignition or computer fault, both beyond me without a laptop and software.
Anybody got any ideas?

Computers don't work like that. It's going to work or not work. None of this "slowly go off" stuff. Now you COULD have a bad sensor, or something like that, but if somebody tells you you need to replace the ECM, and replacing the ECM fixes the problem, then the engine ALWAYS had that problem, or the act of removing it and installing it was actually what fixed it - that is, the real culprit was an iffy ground, or other sporadic electrical connection.

[Shopguy]

Ray's coming over this evening. He's just down the road from me. When I called him the other day he laughed and said "that shits to new for me". I know, me too. I'm gonna pull the throttle bodies off tonight and have a look see at those reeds.