Older Volvo Penta 55HP outboard.

I have this (probably 1980's) 3 cylinder Volver Penta Outboard.
What is likely to be the petrol / oil mixture ratio !

Thanks,

Mike

50:1

It's probably an Archimedes Penta, Volvo Penta is a stern drive.
It will probably have Penta 550 Offshore or similar on it.

BTW, just a bit of history, a 22-ft Cresta Capricorn hull with twin Archimedes Penta 550 Offshore outboard motors named "Penta Cresta" broke the record for circumnavigation of New Zealand by a runabout. 1973 by Brian Pearce and Fred Davis

#2 you have a good memory. I knew Fred Davis, he was a good boating friend of my late father. Fred died in 1979 aged 80, so he was no spring chook when he did the circumnavagation of NZ at age 73.

I remember it because about 1980 I had a 13ft Savage Avenger with a Penta 450 Offshore on the back. Even then, there wasn't a lot around and did a bit of research on them and found out about the record.
They were a great motor and extremely economical and quiet. From memory, at 3/4 throttle I was using about 1 1/2 gallons per hour and ticking along at over 30 knots. They were also rated at the prop, rather than the crank, so a 45 HP was the equivalent to a 65 merc. Well, that's what we were told and performance tended to collaborate this. I remember seeing an ad somewhere that if you could find another production motor that could beat it on economy, they would pay you $1,000 or something.
They were sold under the "Crescent" badge as well. A lot of parts were interchangeable and ours was converted from short shaft to long shaft using Crescent parts. Also the electric start motor was off a crescent. There was a marine dealer in Blenheim who also had a lot of spares. Probably defunct by now.