Hello, New here and need some advice.

Ive been through 2 starters thinking they were the problem and im stressing out over this. It turns over fine with plugs out but as soon as i put 1 in it just "clunks". Not a power problem as I am using an external 12vdc power source. I poured about a thimble worth of injection oil in cylinders but it did not help. Any help would be appreciated.