I pulled the crankshaft out and set it on the edge of a glass table. It slowly rolled back and forth until the conrod journal was at the top, but then when I hung the conrod off the journal it immediately inverted. Considering it didn't even have the weight of the piston and wrist pin hanging off the end of the conrod, it seemed to me the counterweight was much too light.

I tried hacking a piece off the crankshaft next to the conrod journal (i.e. the side opposite the counterweight), like was done at the factory on my Losi 3.4. The engine still runs, I think it runs a little smoother, but I'll have to wait until I can run it properly during the daytime to be sure. Call me crazy but I didn't want to rev a nitro engine on my back porch at 1am.