I had a 4 hp Tecumseh sitting around for years, never used. I had never even fired it off.
When browsing the web one day I came across The Epicenter web site and it described some mounting plates and couplers to use in coupling an alternator to a small engine. I purchased the mounting plates, alternator and coupling for about $150. They have a bracket for side mounting an alternator and driving it with a belt but I elected to go with the direct drive to conserve space.
I have about 8 hours on the generator and it does the job. I've charged the two 100 ah batteries in my trailer at about 30 amps. I'm guessing I could draw more of the generator because the output voltage never drops below 14.2 volts at 30 amps.
The pictures speak for themselves.