[MT nester]

I had a similar problem a while ago. I replaced the rotor and it was a fix!!
As it turns out the rotor was leaking spark directly to the distributor shaft instead of sending it out to the terminals in the cap. I pulled the rotor off and looked in the hole in the bottom if it where it presses down onto the dist. shaft. There were burns up in the hole.
Also make sure the button in the center of the dist cap is not gone.
Good luck.