The International Cessna^® 170 Association

Apologies all if this seems a daft question I’m new at the leaning process
So please forgive this.

Up at about 2000ft trimmed out plane flying lovely… about -1 or -2 air temps, I am a regular carb heat on off etc while keeping a close eye on the carb temp. So I lean out the mixture possibly going lean of peak then back to just rich of peak … it’s a bit of a guess to be honest, but the next time I apply carb heat the RPM hardly drops at all ….. this only occurs when I’m leaned out … is this normal ?

Kind regards and Happy New Year to you all
Paul

No. The losses of ram-air* and enrichment of fuel/air should result in an RPM loss. You might check the condition of the duct-work and scat/sceet hoses as well as the operation and condition of the carb-heat valve itself.

As for leaning procedure on the O300…the Owners Manual gives the procedure I consider best with original instrumentation. Set RPM, then lean slowly until First Indication of RPM-loss…then enrichen back to peak RPM.

Hope this helps.

* It may be possible that a severely blocked or dirty air filter may interfere with this technique, also a wet or iced filter…so be certain of the condition of your air filter. (Imagine if you will: the carb heat applied condition provides an “Alternate Air Source”….so if your filter is excessively restrictive the application of carb-heat might actually remove that restriction resulting in no observable influence of overly-rich conditon.)

Thank You, Im still working this all out ....