Rpm hunting after take off

[Steve Von Gruben]

Hello All, I have a vexing problem on my left engine on a turbo charged Twin. After take off, the rpm hunts about 50 rpm regardless of power setting or rpm setting. Engine is actually changing as airplane is following increase and decrease of power. Engine is running just enough rough to be noticeable but not causing major yaw inputs. Problem comes and goes and eventually clears up entirely about 20 minutes after take off. Problem occurs on both mags. I have cleaned injectors twice, blown out injector lines twice, replaced a suspicious exhaust valve, checked prop air charge, changed plugs, tested ignition leads, checked compression, changed flow divider, swapped tach leads (electronic). Engine is 150 hours out of major and been running fine. I suspect a valve or lifter but hate to start chasing something else until I get a little better idea where to go. What have I missed?

Steve Von Gruben

[N3322G]

Steven,

Oh I chased a similar one for a long time on the right engine. Maybe not the same but here's what I found. Particularly in climbs and descents, couldn't keep the props synced and I could see and hear the rpm change.

Started looking at the Governor. Not that.

Checked all the prop cable bends. Looked fine.

Greased prop cable. Not that.

Finally said to heck with it. At annual had every control cable replaced and the power quadrant disassembled, cleaned and put back together by my shop.

Now the problem has been fixed.

Hope this helps.

[Steve Von Gruben]

As a follow up to my post; with a little more troubleshooting the problem settled into the right mag/ignition system. I replaced the plug harness with a spare and the problem seems to have gone away. The harness that was removed is relatively new with no outward defects and tested ok. Hopefully this is the problem and I will put a new one on after some more flights.

Steve