Jens,

I do not have a PAW engine but I must clean my OS .40 max after about 5 hours of operation because the performance suffers when the carbon collects. But, this engine gets heavy use and has never had any sign of wear.

I did recently damage the piston pin bearing of the connecting rod in my Enya .25 because I did not remove the carbon soon enough. It collected and hardened on the exhaust port side on the piston and head. The engine operated well so I did not know about the lack of clearance at this location. At some point I adjusted the compression inwards--the engine wasn't overcompressed but the piston lacked clearance at just one point in the combustion chamber. So now I have to replace the rod or learn how to make a new bearing.

I also doubt that the oil was the single cause. The kerosene I have been using is intended for heating and may not be as pure as other sources. Some mineral oils I have used actually seem to clean the engine as it runs. I wonder if the larger engines are more likely to build up carbon? My .061 Norvel conversion diesel does not seem to get a build up of carbon. Maybe it spits it out as you describe for the PAW.

I think your original advice was good and I plan to continue to use substitutes for castor oil. I am hoping to have a cleaner engine if I use the modified olive oil and diesel mineral oil mixture.

George