I recently purchased a used Jonsereds chain saw. It is an older model.
What is the proper oil to gas ratio mixture. Is it 50 to 1 or 40 to 1 or
Some other ratio?

If your not shor I would run 32 to 1 a little more oil won't hurt at all

Hi,
With today's gas, 50:1 is proper when done with a name brand oil made to be mixed that way. Do not skimp on the name brand.
Peace,
Clarke

Nab is correct... unless you can verify exactly what the mfg. wants, 32 to 1 would be safe. And use 2 cycle oil only. Regular motor oil will not work. Too little oil will cause either premature cylinder, ring or piston wear... or all three. Post the model number here and someone will help you find the proper mix.