A crank bearing going out will limit the engines ability to rev up. When the bearing starts to disentigrate, the engine will throw little bits of metal around until all bearings, rings and pistons are toast. You better have the crank examined by an expert pronto. If the engine has over 3000 miles, then the crank bearings can go at any time. Especially the PTO end bearing. Broken front engine mounts will cause an engine with bad crank bearings, to bog down and quit when you hit a bump in the trail.