I have a montgomery wards signature 2000 elite (1990)
BS 18hp mod3 422707 type 1510 01, starting problems
the motor turns over very hard it really does not make a full revolution then stops. i have removed the plugs and it turns over very well when the plugs are in its hard. when i put my thumbs over the plug holes it binds. I did a compression test today and they are both at 120psi. I bypassed the starter selinoid and went directly to the ground and positive at the starter with jumper cables (car off) same problem. I do have spark at both plug wires. the guy i got it from told me the oil had not been changed in a very very long time but i checked it and it looked clean. the drive belt is loose but not off i can move it freely. he also told me that the belt pulley broke and had it re welded back on. i checked the flywheel key way it looks fine

 

Sounds like the starter end cap bushing is worn (common problem with that starter). It allows the armature to scrub the internal field magnets and create a lot of drag. Otherwise, it could be a bad battery cable connection.

 

you need the biggest cold cranking amps battery you can get for that engine. I have a 340 in mine