SessionDrummer

I'm not very adroit with the mechanical stuff, so I probably won't answer to your satisfaction. But, here goes.... In the process of trying to diagnose, we had already replaced the engine leads and sent the mags out for a serious once-over (a full overhaul wasn't deemed necessary). Since I was leaning very aggressively during ground operations, and STILL getting some weirdness during mag checks on run-up, my A&P decided to double-check the cylinder compressions (as mentioned, it just sent thru annual in May). Sure enough, cylinder #3 was sketchy. And, then I found a logbook entry from about 500 hours ago where that cylinder was acting up a little bit. But, as far as I can tell, nothing significant was ever done about it. Since I was (very luckily) able to find a brand new cylinder, I decided to replace it. That, along with a minor adjustment with the mixture control, seems to have covered a multitude of sins.

For those kind enough to have offered counsel on this thread.... It would appear that part of my problem was a dying cylinder (which I was surprised didn't come to light in the recent annual). Replaced it, and also adjusted the mixture control under the hood. With those items checked off, and also leaning aggressively during ground maneuvers.... the problem seems to have corrected itself.

Update: The aggressive leaning procedure seems to be working. I thought I was leaning aggressively before, but evidently it wasn't aggressive enough. I'll be curious to see if this proves to be the entire issue, or if there's something else going on.

This is an interesting discussion. Thank you. In all candor, I THOUGHT I was already leaning pretty aggressively for taxiing. And, now if I'm understanding correctly, a couple of you are suggesting that it shouldn't matter (at least in the context of resolving whatever this issue is). Here's another clue: After flying (with all the requisite leaning in cruise), I'll land and then do a run-up to see if anything has changed. Sometimes yes, sometimes no. That has been part of the frustration. It's inconsistent.

Thanks sincerely for this info. I will apply what I'm learning here and see if there's improvement....

No engine monitor. There's a fuel-flow indicator and an old-school cylinder head temp gauge.

Oh, and I'm seeing your other question. Immediately after starting, I usually lean it out for taxi and then go full rich at run-up.

Hi Mike. Thanks for chiming in. Funny you should ask. My A&P suggested that I prime less before starting, but that didn't help. To answer your question specifically: Starting in hot weather, I go full rich and prime twice before ignition. In flight, I lean for 10-11 gph (usually square at 24/24). I sometimes start the leaning process during climb since, in once instance, I noticed engine roughness during climb-out that resolved itself when I started leaning. My previous time is all Cessna, Piper, and Diamond. Trying to learn the quirks of this aircraft and engine.

I bought a 1977 M20C last year, and I'm a first-time owner. Just did the annual. Prior to that, the mags had been running rough during run-up and were due for a 500-hour. We sent them out, and no overhaul was necessary. But, they got a good once-over. My A&P was comfortable with the result, and let the plane out of maintenance. But, by my second flight, the run-up was rough again. Sent her back to maintenance and replaced the ignition leads. Everything checked out with the mechanic, and they ran smooth on my first couple flights. But, sure enough, they're running rough again. The mags are Bendix, and the engine is the 0-360-A1D. I'm starting to wonder if it's something else. Any ideas here?

Following this thread. I bought a 1977 M20C last year. It's currently in annual, and the dreaded tank leakage might be starting to present itself.