I can't say for certain on chainsaws running a little isopropyl in the gas, but when running a 4-stroke on methanol, a great deal of heat is absorbed trying to vaporize the fuel...carbs and manifolds may get frosty. That can be real good thing in a way because the cold, dense mixture can pack in a bit more densely, but keeping that alky dry is paramount because when the temp of the fuel-air mix drops low enough water can precipitate out as ice crystals.
Guess what happens when ice crystals hit hot engine components? At best, there are microscopic bursts of steam, which may interfere with ignition or flame propogation. it can get a lot worse.
Most of us change the flappers so we can get hot air to the carb when the weather gets cool. It hlelps warm up faster, but keeps the saw alive longer too.
Back in the old days of snowmobile racing, many snowmobiles' engines were visible, right in front of the rider. Many riders, not just racers, put aluminum velocity stacks on their Tillotsen HD carbs, partly because they looked cool. Sometimes unscrupulous racers would grab handfuls of snow and try to throw them at the carb or carbs on an opponent's sled. Sometimes this would mean the momentary loss of a cylinder, and sometimes the permanent loss of one. In 1968, I saw it precipitate the loss of 3 teeth!
I think the point is, don't throw snowballs...not at another racer, and not at a hot piston.
