Agree with IO540 about the data. Had a partial carb ice problem years ago and more recently when flying over very inhospitable terrain a rough running engine. Immediate action was set best course for nearest airfield (LBA at the time) and then sort out what may be wrong. Stabilised engine with less than max revs and landed safely. It turned out to be a suppressor shorting out a mag. DID NOT DO A MAG CHECK until safely down. Always taught not to as if that is the case and you get a dead stop then when resecting the good mag a lot of damage can result from unburnt fuel / air mix.