why won't my mtd b&s 14hp ohv ic engine turn over>?

my 97 14hp 42" cut b&s mtd mower will barely turn over. I have replaced the ignition switch, the solenoid and the battery, but all i get is a bump and every now and then it will spin the engine a full turn but not very often. are there any suggestions ? The previous owner let his yard man use it and he disabled the auto shut5 off when you get off the mower but other than that all is wired as it should be