merugo,
I made 2 batchs of the modified "cheap cooking oil" and then was sugested olive oil by an aquantance who is a bio chemist.
In actual engine tests both batchs of cheap vegi oil ran well and mixed well but there was increased mechanical noise from the motor indicateing a lack of viscosity at running temps/conditions, wereas the modified olive oil the improved running/starting qualities were still obtained but the mechanical noise had disappered -(engine sounded the same as if running on castor)
I also noted that running on modded olive oil had a cleaning effect -ie all the burnt castor residue on the piston was flushed out , initial runs had a very black gooey exhaust , but once the engine internals were clean the exhaust went clear and the inside of the motor is like new. Hence my recomendation not to use modded olive oil in an old well run engine as the cleaning of the castor varnish may result in a loss of compression.

Slope-soarer,
Your mineral oil results are interesting , what brand/type of oil are you useing???
as some have tried mineral oils /2st oils with mixed results, I think the results depend on the additives the oil has , some seem to interfere with the combustion process some dont , maybe we need to tabulate those mineral/synthetic oils that work.

Andy,
From what I have read about castor oil is, first press castor(degummed) will not mix well with petrolium/kerosene, but heating the oil for a period of time will partly polimerise the oil , this changes its structure and it will now mix with petrolium products above/about (ithink)20degC-sorry i cant remember the No's, from this I beleive Klotz castor has undergone this heating process dureing its processing.