I've never done it but i imagine it's probably a bit cooler then a lighter, but i would be freaked out if i was already really high with a soldering iron like 3 inches from my nose lol.
Terrible idea. Imagine how easy it would be to burn your finger on the carb with the iron. That would burn like a motherfucker. Would be pretty easy to do if your baked too.
Speaking from experience, yes it burns like a motherfucker, but the worst part? The smell of your cooked skin, makes you want to gag. I grabbed a soldering iron that had been on for 2 days straight and I didn't even smoke back then.