The Yamaha Seca II is powered by a carbureted, air cooled, 599cc four-cylinder engine which runs relatively low compression. The Seca II is rated at 61 HP at 8500 RPM, at the flywheel, from the factory. Assuming 15% loss through the chain drive system, that's 52 HP at the rear wheel.
A well-tuned XJ600 with stock exhaust and airbox is expected to produce 48 to 50 HP at the rear wheel. Here are the Seca II's full factory specs.
In 2010, we did run a Seca II on a dyno. This particular Seca II had a UNI filter, 102.5 main jets, #20 pilot jets and a 4:1 Yoshimura exhaust. It appeared to be running rich during each run. The results of the dyno run are as follows:
- Run #1 44.67 hp
Run #2 46.70 hp
Run #3 46.12 hp
