A few years back, I departed Glasgow Airport for the journey south over Beattock with the cloud just above the summit. OAT on departure was +4 deg.
As I climbed, I realised the engine wasn't revving as high as it should, and thought I could detect, or possibly imagine, a slight misfire.
Fortunately I was driving my car, so I was able to pull into the first layby I came to, and as I pulled up, there was definite black smoke from the exhaust accompanied by a misfire. Classic carb icing symptoms of course; I was using a lot of throttle on the climb and was about 1000ft amsl, so the inlet throat pressure would have been very low causing any moisture to condense and freeze.