I have a 1990 Johnson 200 GT. I've run a compression check on all 6 cylinders. The readings where between 80-85 lbs on all 6 cylinders, which is far from where they should be around 100lbs-psi. I took a second set of readings but this time I put about a teaspoon of 2 cycle oil in each cylinder and the readings went up to over 100 lbs- psi on every cylinder. I removed the heads to inspect the cylinders. The cylinders look good considering the motor is almost 20 years old. There was some minor scaring on the cylinder walls but not enough cause the engine to lose 20 lbs of compression on each cylinder. While I had the head off I also put a new head gasket on and repeated the compression test with the same readings , 80-85lbs.My question is how much weight do I put on the fact that the oil in the cylinders raised the compression. Would this suggest that I need a set of rings. My thought is the oil sealed around the piston causing the compression to increase, but with out the oil I'm losing compression. Maybe I have bad compression ring or maybe after 20 years I need new rings. I would be thankful for any suggestions on my theory.
