Well, it is free to look at the linkage
Check it out, and try to figure out if it is sticking. Look right down the throat of the carb to see if the blades are staying a little open. Do you have any WD40 or anything like that? That will work, too (just not as well). Carb cleaner is around 5 bucks.
A place like Autozone can likely loan you the tool to hook up to check timing/idle speed
