[carlmadams]

I have a 1997-98 Yamaha 70C. Motor was running fine, but while at speed (4300 RPMs) it immediately slowed to around 3000. The sensation was as though I had run over something that fouled the prop. It did this after only about 30 seconds of running so I don't think it was an overheating related issue. The motor will rev to 5000+ rpms when out of gear. Did not sound like a dropped cylinder. Plug wires were tight. My first thought was a spun prop hub, but I think that it would cause a loss of bite while rpms would go up.

Has anyone had a similar experience with this motor or similar. This is the same basic motor as the Yamaha 90?

[windknotnc]

Sounds like a powerpack (CDI unit) to me. The only way to test is to take it to a Yamaha man and let him connect it to a meter or computer and diagnose. This unit controls spark advance which could come across as loss of power. If you have to replace you are looking at $450-$500 but not much labor because it is a bolt on and plug up part. Good luck.