Two additonal thoughts on carb heat use:
If you have chosen to use carb heat, consider doing the following right away: Reduce the throttle setting somewhat, to reduce the total mass airflow into the engine. This reduces the amount of heat which will be needed to raise the temperature of the air in the carb, and the metal carb parts themselves. It also reduces the total amount of moisture being sucked in. (this is a good reason for having an idea of the minimum power setting your aircraft needs to maintain altitude). Once set at this power setting, lean the engine as much as practical. Bear in mind, that for most engines, the power setting will now be in the range where leaning to peak is acceptable for continued operation. The hotter the exhaust, the hotter the carb heat air. The less volume of intake air, the hotter a given amount of carb heat will make that intake air.
If you're using carb heat, turn off cabin heat. Other than for aircraft with combustion heaters, it all comes form the same place, you may as well get as much as you can where you need it most...
Having flown behind VW and Continentals I am manic about testing for carb ice, having the donkey stop or perform badly a number of times through icing
I take a very simple view of prevention.
I've seen the ice form on the carb housing and supports on a hot sunny day!
I overuse the carb heat control if anything and leave out it for longer. It astonishes me to see other pilots use it only on take-off and landing and then only for a max of about 5 seconds.
I am on the alert for signs of icing and will taxi on hot, only returning to cold when lining up. In the air I will add power before using the control to warm the engine before hand and I'll usually fly at a higher power setting than normal so as not to risk icing at the butterfly valve.
The real problem comes in the descent - in icing conditions you never just chop the throttle but keep power on for as long as possible - in the 3 cases where I sat looking at a plank of wood whilst still in the air, all three were at short finals.
Its also worth noting that because of those experiences, most of my approaches are higher and closer in than other pilots so I have a fighting chance of gliding in.
It horrifies me to see the low dragged approaches some pilots use..
In short though, everyone should get to fly an 'ice-maker'. It will change your views about carb icing
