I have a mtd lawn tractor 38" 7 speed 12hp briggs & strattion eng model# 130-650f
I am having a problem that when you put it in the forward position and release the cluch it pops out of gear but when you put it in reverse it stays in gear. I change the transmission belt but it is still doing the same thing. Does anyone have any ideas what it could be.

Hi,
I would say that it is a worn shift collar on the forward side. Your machine is an older machine(that third digit means it is a 1990 model.) The part is available as a part, but is not fun to install unless a practiced mechanic since the transaxle must be removed and disassembled.
Peace,
Clarke