I have a Kawasaki V Twin FH680V with about 300 hours on the engine. This spring everything was going fine (not a commercial user but using a commercial Husqvarna mower) last week my engine lost power about 20 minutes into the job, my RPMs fell and the engine struggled to continue mowing. After 24hrs rest the problem comes back again in 15-20 minutes. I have changed the oil, oil filter, plugs, air filter and gas filter with no change. Being a non mechanic my only thoughts are gas line blockage or a carburetor problem, any ideas?