Welcome to the site buddy! If you need any help with skis or rides in your area just give me a shout.
It sounds like it could the the voltage regulator. Disconnect the red wire and see how she runs, if it smooths out replace the voltage regulator. Unfortunately to see if this is the problem you'll really need to ride it, but you should get a good indication on the trailer.
Also do you still have grey fuel lines? If you do you'll need to replace them and overhaul the fuel system. Also check the compression.
Lou