1988 883, ran fine then acted like battery (new) was going dead or starter failing. WOn't turn engine over with spark plugs in. Starter OK according to rebuild shop. I reinstalled it, used car battery directly to starter...solenoid pulls ok, motor wont turn engine as long as plugs are in! My tests used direct wiring so I've bypassed any possible bad connections, etc. Are sportster starters known for somehow becoming 'weak'??

 

That's a tough one, for sure. If it turns freely with the plugs out, it sure seems to be a starter problem, although I don't recall having heard of one that "bench tests" OK totally bogging down under start load. Did you do anything else coincident with the problem...change oil to heavy weight, change timing...? Wish I could offer more help. Keep a check here, 'cause there's some experienced folks scratching their heads right now to offer good suggestions. Keep us posted, too, as you work through this.

 

I really wish he had posted how he resolved this. I have the same issue and am stumped.