Outdoor Power Equipment and Small Engines - Craftsman YT16 Twin runs up and down

Hi everyone--
I have an old (probably 1992!) Craftsman YT16 Twin with the Kohler engine. When I tucked it in for winter I put Stabil in the remaining gas and it has a new/replaced carburetor last year.
When I started it up for its first mow it did just great, then it started doing this bit where the RPM runs down, then back up, then back down, a full cycle up and down every few seconds.
it only ceases this, when you run it up to higher RPMs and may be I just can't hear the cycling at higher RPM. It sounds like something is wrong with the governor? Any ideas out there?

It's a common problem with that engine. In the very front of the carb under the air filter area is a mixture screw. Try backing it out 1/8 of a turn or so. That will probably stop the problem, but if not you'll need to remove the top of the carb and clean out the carb, and remove the main jet (accessible through the drain plug hole at the bottom) and clean it out, and clean the area behind it.

Don't know if you did or not, but next time you add stabil, run the engine for a few minutes to be sure stabil is also in carb before storing.
Mike