65 M20C AOG Carb Heat cable broken at the level arm

[NicholasM20]

Aircraft left at the airport and rented a car to drive 4 hours home

Yesterday when I used the card heat at 5500ft, i could pull the control rod in the cockpit out more than it used to, but engine runs fine and landed safely. Did a quick test, carb heat no longer affects RPM.
Opened up the side cowling and found the problem...the cable is no longer connected to the level arm..

Looking at the O360 doc online, although not the same setup, looks like the cable is passed through the level arm bolt and bend 90 degrees, and tighten the bolt.

 

I’d like to find an A&P and address it, a couple options:
1. as simple as passing the remaining cable through the bolt to secure it and bend 90 degrees
2. or somehow safety wire the carb heat lever arm to make the butterfly valve open all the time, so i can fly home to fix it

I would appreciate if you have other thoughts and suggestions!

[N201MKTurbo]

You can probably get away with just putting the end of the wire in the pivot bolt and readjusting the conduit clamp.

[NicholasM20]

Thanks! A local A&P helped me out by reconnecting it like this post. The cable was broken, so it's a bit short, thus the valve didn't open all the way (to allow carb heat to get out) when carb heat is off. The fix worked and was able to fly home safely. Will need to replace the cable.

 

 

[47U]

On 9/7/2025 at 1:57 PM, NicholasM20 said:

I would appreciate if you have other thoughts and suggestions!

Consider asking your A&P to add the hose to the carb heat dump valve.  The hose is routed to the left exhaust cavity and gets the hot muffler air out of the lower cowl.

And the linkage wire to actuate the dump valve looks a little banged up…

[jamesm]

interesting on my 67'C the smaller duct shown in your picture is just capped off. wonder what made them decide is or isn't needed and what is it's purpose?

[47U]

2 hours ago, jamesm said:

wonder what made them decide is or isn't needed and what is it's purpose?

I’m speculating… originally Mooney thought that air flowing through the heat muff would lower the muffler temperature, perhaps extending the life of the muffler (?).  It is odd, though, that the factory decided to just weld a plate over the outlet to close off the exhaust valve.  And then keep the double linkage through the dump valve to actuate the carb heat?  Doesn’t seem very well thought out.  (Or, maybe the picture below was modified after it left the factory?)  They must have had a bunch of the old air boxes in stock and used them to save money, rather than redesign the carb heat system without the dump valve.

[Jim Peace]

There is a MSC in the northeast that removed my entire carb heat system....so it's probably not needed....

[Hank]

7 minutes ago, Jim Peace said:

There is a MSC in the northeast that removed my entire carb heat system....so it's probably not needed....

When it broke on my C, it defaulted to Fully On. In flight. It was a very s-l-o-w flight home to figure out what was wrong . . . Even Atlanta Approach asked if I.was really  Mooney. 

[NicholasM20]

The connection is fragile, just a bolt and nut to squeeze the steel cable to secure to the lever arm. Why couldn’t the design be more like throttle/mixture/prop where it’s secured, considering this is a critical component to prevent carb icing…?

[NicholasM20]

2 hours ago, Jim Peace said:

There is a MSC in the northeast that removed my entire carb heat system....so it's probably not needed....

I needed to use it as my engine runs rough near the ocean, that’s when the cable broke when I pulled on it…

[highflyer77]

Imagine, you will have to use it what it´s originally made for... I would be interested what MSC takes responsibility to withdraw a carb heat system at a aircraft with carburator engine ...