I have a problem with my snow blower (Sears, 8.5hp), which I
bought a few years ago and use maybe 2 or 3 times a year. When I
start it, it seems to be running rough, it almost seems like
it's going to stall (and if I adjust the clutch too much, it
does). What's strange is, when I get into the snow, it picks up
immediately and runs smoothly, shooting the snow 20+ feet. When
there's no snow, it goes back to running rough.

I asked my friend who is usually good for solving stuff like
this about this problem, and he told me that his snow blower (an
expensive brand 9hp model) has the same problem, and that his
repair guy has not been helpful in trying to solve the problem
over the phone (presumably he wants him to bring it in for
service).

What could be causing this? I know I should probably have it
serviced since I haven't done anything to it since I bought it a
few years ago (but I've probably used it less than a dozen
times), and probably will have it serviced this spring/summer.

Bill