Cessna 120-140 Association

is it better to leave power at full throttle and apply carb heat, or as i did... apply carb heat, level off, and reduce power to cruise ? Appreciate all the great advice and personal stories

Welcome to the Assoc. and being a new owner Bill. The long time pro's sound like they have your answer. I'm in northern Illinois and have had the wake up call with carb ice several times. Like stated leave your carb heat on long enough to clear all the bad stuff never run partial carb heat and make sure your heat air box is in tip top working order. Not sure if carb ice reacts different to Marvel carb vers a Stromberg but we have a Marvel . Glad your getting answers from long time runners.

Thanks for all the great feedback everyone! I had a great flight over the weekend and got to use the new (to me) knowledge. Temperature was about 28F at 2500'MSL with dewpoint around 24F. Cruising at 2400rpm, I had to clear ice from the carb about every 15 minutes or so. I'd start to notice the engine starting to run just slightly rough, pull full carb heat on, and open the throttle up to about 2500rpm. I let it run that way for about a minute or so, then turn carb heat off and reduce throttle back down to 2400rpm. Then it would run smooth for another 15 minutes or so. It seemed to work and be repeatable, so I think I'm happy with that procedure. I also think I'm catching the icing early since what I noticed as roughness didn't get worse with application of heat, but sure got better after doing so.

I'm over 300 hrs in my 120 and have never experienced Carb Icing in it. I've only experienced Carb Icing once or twice in 20 years of flying little airplanes. Lucky me I guess!

Are you running Auto Gas or 100LL? Stromberg or Marvel Carb? Its curious that you have a consistent carb ice "problem" when so many of us fly in similar conditions and don't get it.

i have a manifold pressure gage installed and one see's ice sooner than a rpm gage

i have a manifold pressure gage installed and one see's ice sooner than a rpm gage

Now I know what to do with mine, always wondered why a previous owner put it in, been using it to set cruise rpm with mixed results...seen here pre-restoration-

My carb is a stromberg on the c85

Is there any significant difference in icing between the Marvel MAS3PA and our standard
Stromberg carburetor?

tonycondon wrote: ↑Wed Nov 30, 2022 10:41 am I'm over 300 hrs in my 120 and have never experienced Carb Icing in it...

I think if you use carb heat religiously whenever you reduce power below about 2100 RPM you'll rarely encounter carb icing. In about 35 years I can only remember 2 instances where it was a real problem.

An ounce of prevention, and all that...

Something I would like to hear others opinions on is my my primary flight instructor has always told me to never pull carb heat on during cruise or high RPM as it could lead to detonation. If I've wanted to "check" during cruise, I've always pulled the RPM back first before pulling it on. Anyone else do this?

So far the only time I've encountered engine roughness associated with carb icing in my stromberg equipped c90 is at the carb heat check during ground run up. Have pulled it a few times and the engine has almost died, before the RPM slowly rises back up. Always check before take off.