poulan pro

Hi, I bought a used Poulan Pro Riding lawn mower (model PP11536LMB) and am having some trouble with shifting. It shifts just fine when the engine is off and the clutch is not pressed, but when I engage the clutch, the shifter will not move. Any help is appreciated, thanks.

Just rebuilt a neighbor's PP20VA46 that had a blown engine. Replaced blown B&S Intek 20hp engine with identical model, drive and deck belts replaced. Engine starts and runs well, but when I press on the forward drive pedal there is a slight forward lurch, prior to the mower moving forward, and...