I have been given (yes!) a Crescent 4 outboard, which is the 1970's version of the Volvo Penta 3.9 / Archimedes 4HP. This example is an external long range fuel tank version, but with no tank. I am hoping to get it running with a very small internal tank I can just about fit under the hood - my dinghy is very small.
I too would be very, very grateful to anyone who could supply either a scan of the relevant manual, or just details of the fuel mix, spark plug type and gap, points gap, timing etc. I have recently found a link on the web, which it seems I'm not allowed to post here, but it appears in Yachting and Boating World Forums - which may be relevant - and I hoped including it here might help someone. I was going to try it out with a 25:1 mix, so I've been saved from that mistake, I hope. That forum says the Volvo Penta 51 (5 HP similar motor?) runs on 50:1, so I will try that out when I find a new spark plug to fit.
My boat is a home-built 8 foot pram with standing lug, so I would not welcome a tank under foot at any time. I also have an old British Seagull 40+ from 1954 - nearly as old as I am, but have yet to try it out on the boat. The Crescent is lighter and cleaner, and may be better as it seems in good condition. I hope I can get it running.