The compression is around 9,3 and 9,7. I'm not sure about the pistons used, all I know is that she got a replacement engine at some point. I will open in- and outlet, try to see something with the endoscope and will post pictures.The Commando uses the projected nose spark plugs Champion N7YC or NGK BP7ES
Champion N7YC - alternative spark plugs
www.sparkplug-crossreference.com
Even with an 1/8" skim off the head of a bike I built I didn't have spark plug clearance issues. You can see the tops of the pistons through the spark plug hole to see if you have a contact issue. Do you have stock pistons? with flat tops and have valve pockets in them. I would remove the carb and manifold and the exhaust pipes to let you see more of the areas where trouble could be. Are there any loose parts or missing screws / bolts in the exhaust or intake system. Do you have good and similar compression over 150 PSI in each cylinder??
Aside from that I bought a digital TDC tool to see if one spark plug sits deeper than the other or one piston goes up further. Maybe It is just a thread issue.
Updates on monday!
