If you want to try a test fire, here goes:

Fire the thing up using the crank, get it warm. Use a volt meter to
check the polarity of the output as well as the voltage. Shut it off,
hook up some jumper cables to a SINGLE 12 volt battery, maintain
positive to positive, neg to neg, see if it spins. Be ready to pull the
jumper cable off at the first signs of it firing. Use your voltmeter to
check and see if you have the same voltage as before.

If you totally screw up, you may need to reflash the field, instuctions
are in some of the other SA200 manuals, you'll just have to download
several and look.

I doubt I'd convert to LPG, not worth the trouble. I've never had
gasoline related trouble getting old tractors to run, even with ancient
gas. Bad spark can cost you days of fiddling around. Sounds like you
have a gas tank problem, full of rust and crud. How about taking the
tank off and either full rebuild or replace? Or perhaps an auxillary
tank that is much bigger than the one on there? As far as that is
concerned, there is a fuel pump block off sitting under the exhaust pipe.

If you are looking for engine info, try posting on
http://www.ytmag.com/
Parts at
http://www.ytmag.com/cgi-bin/store/search_parts.cgi

Can I ask what you need 40 volts DC for several days for?? Certainly is
not welding!!

BFR wrote:
You're right, it does have a magneto. This reply also goes to Clif who
asked about just using the crank. The problem is that this machine is
on a ranch and is rarely used - when it is used, however, it needs to
start and work hard for several days. If everything (meaning the
carburetor and the gravity feed fuel system) is right, it will, as the
old timers say, start with one or two cranks at "15 degrees F and a 40
mph wind". I am forever having to rebuild the carb and clean out the
fuel filters so I am planning to convert it to propane (someone gave me
the parts and I know how to do it). With lpg it starts readily, but
you have to crank it over fairly fast maybe 20 or 30 times without
stopping so the vapor will be drawn into the cylinders and that's a
little hard on the old arm especially considering the potential for
busting one's thumb or arm; once it starts on lpg it's great, no warm
up or anything. The code number for the machine is "671" and the
serial number is "A188912". The manual says this about excitation:
"Separate excitation of generator shunt fields is supplied by an
exciter which is direct connected on the commutator end of the
generator. The exciter armature is mounted by a sleeve connection on
the same shaft as the generator armature."

Assuming I hook it up wrong and the engine starts to turn backwards,
will that hurt anything as long as I kill the switch as soon as I know
the direction? It shouldn't take more than a half revolution or so to
know.

Thanks for all y'all's help.