Erratic Loss of 200rpm On Climb Out

I had a similar sporadic RPM drop with my C85 (1948 415-E), turned out to be excessive play in the exhaust valve guide on cyl #4. With the valve cover off if was apparent by wiggling the top of the valve that there was too much play. I changed out the cylinder.

Randy Hirsch

Look into the beginning of sticking valves.Have you ever heard the term morning sickness.It is the first flight of the day the head is still cold and the exhaust pass is hot and that is were the exhaust valve guide protrudes.

Hello, thank you for the replies. It was on a moderate climb with high weight.

Denis, did the problem occur in steep climb or in a more shallow climb?

Here is an interesting story from an AOPA safety brief:
On a mid-June morning in western North Carolina, a flight instructor and the owner of a Cessna 182 ventured out for a training flight . A weather station reported visual meteorological conditions (VMC ) with a temperature of 80° F and a dew
point of 45 °F. The relative humidity was 28 percent. Shortly after departure the engine lost power , and the pilot attempt ed to stretch a power-off glide to a nearby grass strip. The airplane impacted tree branches before it stalled,
and subsequently impacted the runway environment. The NTSB determined one of the probable causes of the accident to be carb icing that led to a loss of engine power.

Carb icing can occur at almost any temperature and humidity.

I also live in Florida and have run into carb ice. The symptoms are the same but I have never heard of carb ice with the ambient temp above 70 degrees. Mine occurred at 2500 feet and eight miles from the airport. I immediately turned toward the airport and pulled on the carb heat. In 45 seconds, the roughness went away and I went back to normal (carb heat on) rpm.
A Suggestion: Fly later in the day when the temp is in the 90s. My airplane would still climb with the carb ice but it IS scary.