I have a 36" Encore walk behind mower that is 5 yrs. old. It has a 14 hp Tecumseh motor that runs perfect. The problem is the machine will leave an uncut strip of grass down the middle between the two blades. I have replaced the belt, the bearings, blades (from OEM), spoke with a tech from Encore who suggested lowering the blades down to the deck height...none of this has helped. Any thoughts on where else to look for a problem? Has anyone out there had a similar problem with their 36"?