Hammer,
I was using a 18% castor/syn. blend for oil.
I really think the problem is in the piston or the sleeve. When I took the back cover off the inside of the block looked clean and the bearings felt smooth once the piston was freed up. However, when I looked inside the exhaust port I saw what looked like small specs of carbon in the sleeve openings and on the top of the piston. I wonder if the after run oil is loosening some of this grit and lodging it on the piston.
So, do you think this is from too much nitro?
I appreciate your thoughts.