The International Cessna 170 Association

Vertical wrote:If I level out it gets smooth, and engine will soon redline (because I’m still full throttle)

It never happens in level flight. Only at steeper VX /aggressive climb attitudes.

Check the carb float-level setting. If it’s incorrect then it may be flooding at high pitch attitudes? (This is a WAG... I’ve never experienced it personally, but am using my imagination.)

I can only think of two possibilities where having a load on the engine would cause your issue. Your sparkplug wiring harness breaking down and allowing a short to ground under high loads. This can be checked with a high tension lead tester. The second is a worn out set of engine mounts. They will compress under load and not isolate vibrations.

gahorn wrote:The diverter was a sheet-metal baffle riveted in early sumps but later sumps had it molded in the casing. While I haven’t seen this defined, I believe it’s another difference between the early sump and the later so-called “5-bolt” sump. The diverter is not illustrated in the parts catalog.

It appears there must be at least three iterations of this sump. I have a sump from a C-145-2 without any diverter/baffle. There are also no rivet holes indicating that there was once a baffle there. The picture is taken with the sump upside down and a light shining down through the intake where the carb attaches.

Well, I pulled the cowling and the air filter, poked prodded and visually checked ops of airbox, intake and just about everything else. It all looked good with the exception that the 4 through-bolts holding my air filter on were loose, and have probably been that way since the filter was replaced at last annual. The rubber gasket appeared to be holding it all together with no air gaps, but hard to tell what might happen in flight. I can't possibly see how air leakage here would cause roughness in any possible way however.

I put it back together and assembled the smartest mechanical minds I could find at the airport for a test flight....It ran perfect. No roughness. We did lean mag checks in cruise, under loads, carb heat and leaning in various combinations etc. No issues...Had a voltmeter hooked up in cockpit to monitor.. All normal..

Weird.

Thanks for all the suggestions. In the clear for now, but we'll see if if it happens again.

What were you looking for with the voltmeter? Connected to what exactly?

gahorn wrote:What were you looking for with the voltmeter? Connected to what exactly?

Voltmeter was connected to the alternator via the circuit breaker. This was less to do with the engine roughness, and more curiosity of the SCB 201-CV alternator that's installed via field approval. This is a 6.5 lb unit that was available for install by STC on franklin engines (and marketed to continentals), but apparently made it on my plane as well. Maybe a bit of an oddity, but it has worked flawlessly since 1994. It has a small oil leak at the case, but until it shows signs of worsening, i'm not going to touch it.

Ever heard of this unit?