A Yamaha 760 was brought in recently with electrical issues. The customer stated the ski would charge and stay running when “they thought” the battery or another component would lose connection, after setting it would start back and operate properly for a short period of time.
Compression check / Diagnostic’s
After inspecting the ski we found that the rear cylinder lost all compression and the spark plug tip had a metallic coating and was pushed inwards. We pulled the cylinder head to confirm the damage.
The rear piston was seizing and would lock down the piston to the cylinder wall. While seized the entire system was locked down hence the electrical issue, pushing the start button did nothing and that’s why it felt like the battery was dead or something lost connection. After cooling the piston would release and the ski could be started again until the next seize shortly after.