ORIGINAL: DesignMan
One other thing to check is varnish on the cylinder walls. If the inside of the bore is medium brown or darker, use 0000 steel wool or the bore brush sold by Davis Diesel to clean it back to bright metal.
The varnish actually gets sticky at running temperature and causes all sorts of bad running and overheating.
No, it's clean as a whistle inside with no sign of castor-oil gumming -- which stands to reason since this is the first time I've run it on castor-based fuel :-)