Could be several things, Steve. Is the air filter clean? How about the fuel filter? Usually when an engine "hunts" it's a fuel problem...running too lean or too rich.
If the filters look ok, when it does this again, try applying partial choke. If it straightens out, you may have crud in the main jet.
I had that problem on a few of my 24 hp hondas. I simply broke down the carb and cleaned it all out real good and changed the fuel filter and all was good..
after being told to pry off bowl the problem was the iner o ring dry hard crumbly replaced with similar one and all is good (found o ring peices in carb<was told it was because motor sat for 2 years and dryed out before i got it) thanx again steve