Johnson Iron Horse Generator

Just got this little Johnson Iron Horse 12v generator today. Have been eyeing it for a long while, being an 1800rpm unit it would be nice for running an inverter at shows.
Anyway, just got it inside tonight, checked out the control box, and tried turning it over with the generator/starter.
When power is applied, and the starter is pressed, the engine promptly binds up tight, and the ammeter pins to the -.
After pulling the side cover, I found one of the field windings completely loose.
I have about zero experience with generators like this. anyone around here have one similar?
Nervous to break it even worse, been wanting a low speed generator of any sort for a while now.
Full Description: Johnson Iron Horse (1935) The operator’s manual (sometimes referred to as the owner’s manual) is the manual that came with the Engines. It can be compared to the manual you receive in the glove box of a new car. This manual gives the owner-operator instructions, shift patterns, capacities and adjustment procedures. JKEE's List of Engines! Engine Number: Manufacturer: Model: Serial Number: Year: Condition/Parts Needed: 1: Johnson/Iron Horse: X-448: 87835: 1944: Running! Taken 7 download on pc.