A carb heat trick
I was talking with a client today, who is the chief pilot overseeing a flock of 172's which are used for survey. One of his pilots (a 1000+hr guy) had just limped away from destroying a 172, following a forced landing. Apparently the engine pretty well ended up in the passenger's seat beside him - lucky guy, other than I suspect he'll be looking for new employment.
There was some discussion that perhaps carb ice had been a factor in the engine failure which preceded the crash. While discussing carb ice topics, I mentioned a trick I was taught, and I was a little surprised that he had not been aware of this, so maybe it's time to present it again.
If you have decided that you need carb heat to deice the carb, you need lots, and you need it quickly, 'cause things are getting worse in the mean time. To get the most of the heat available from the engine, into the carb, after applying carb heat (and worrying more, 'cause now it's really stumbling), lean the mixture to achieve the most lean setting you can manage without making it run worse. You're not developing full power with carb ice anyway, so you're not going to damage the engine by overleaning it. The presence of carb ice will have enrichened it anyway, but leaning it to "normal" and thereafter to peak lean will result in more heat from the exhaust, which turns into the carb heat that you need.
As the carb heat begins to have an effect, consider flying at a reduced power setting (and leaning more if need be), as less volume of air going through the carb at the lower power setting needs less total heat to warm it and melt ice.
If you have an aircraft with a carb air temperature indicator, watch it as you do this, and the affect will be obvious. A CAT indicator is a great investment.