Hello Cam
Probably a good idea to check the valve clearances as well. Being a side valve you have to physically remove the valve to adjust clearance.
With the castrol R, castor oil does 'gum up the works' a little bit so it would probably be a good move to pull the cylinder head off and take a wire brush to all the deposits that have formed (they would have formed anyway but there is probably a bit more that usual.
I have been meaning to start adding valvesaver to mower fuel but haven't gotten around to it. In the early 1980s briggs released an internal service document that stated, it effect, there is no gain from adding lead to homeowner machines as most won't last long enough for it to prolong life any, and commercial machines with stelite valves benefit from not being gummed up by lead.
