A clogged (or bent shut) exhaust can cause low compression, but not on just 2 cylinders (not on that vehicle at least, unless maybe you have headers?), and certainly not from “carbon in the pipes”. Short of you having 2 header pipes that are collapsed, the best way to find out for sure why you have the low compression would be a cylinder leak-down test. As an example, a friend of mine bottomed out his car real bad years ago, and squished a bunch of his header tubes. It ran terrible until we got that fixed. Didn’t bother with a compression check, since it was pretty obvious. But I’m sure it would not have been good!