I think perhaps my problem is the 2 1/2" aluminum spinner. I tried using the starter on my smaller .40 and it works fine, even on 24 volts. I'm guessing the starter cup won't slide far enough onto my larger spinner so it gets off center easily. I tried pushing it on the spinner harder and even took the plug out to see if the engine compression was a factor...it wasn't.

Does anyone know of larger cups that will fit the dynatron? Where can I get one?