A picture would help.
There was a Johnson Iron horse which is a small air cooled engine often attached to a generator, these were made in America and I believe manuals are available in the US if you search on the web.
Hi Philip. I haven’t actually got the engine here yet to take a pic. As soon as possible I will. Yes it is a Johnson iron horse 514 series I believe. Thanks for the info.
Another option is to try some of the Govt surplus stores , those that have been going for some time bought hundreds of these , and numerous spares..well worth a try.