I bought a used 1974 Yamaha SC 500 back in 1978. The ones friends had had were always seizing up. The guy I bought the bike from told me the trick to keep the beast from seizing was to mix the gas and oil at 10 to 1 instead of the standard in those days, which was 20 to 1. I followed that advice and it never seized on me. The guy I sold it too later reverted to 20 to one thinking it might have more power that way (it doesn't, by the way) and seized it up the first ride.
The bike had terrible suspension, even for its time. It steered fairly well though. It was peaky, but when it came on the pipe, it hauled ass. Standing start drag races against a 1976 Yamaha TT 500 4stroke and 1978 Suzuki RM 400 on pavement would have both the TT and the RM getting a huge jump off the line and way ahead before I could really get moving. The straight we were on did not allow me the time to catch them, but it was gaining on them. However, from a 2nd gear roll-on, the SC would smoke either of those bikes. Well, it would if you did the race not too long after the SC had been warmed up. The SC 500 looses power very badly when it gets hot. Example: We had a huge sand dune that was smooth enough to get a run at, but very tall and steep. The TT 500 couldn't even make it although the RM 400 could. The SC 500 would top the hill in third gear easily if just warmed up. After and hour of mid-day summer riding, however, it didn't have the power to pull the hill in third and had to be downshifted to second and would end up digging a hole and sitting in it well before the crest of the hill, just like the TT. Let it cool down again, and it topped the hill in third effortlessly. The RM 400, by comparison, didn't exhibit much difference no matter how hard and long it had been ridden before trying the same hill. Once the SC 500 was moving, it had good acceleration for it's day, very good. My IT 465 Yamaha enduro (1982) I got years later, however, would beat it even in roll-ons and had smooth power everywhere. Comparing the SC to that, it was a terrible machine. It was fun at times, however. Not many bikes before the advent of the YZ 465 could stay with it in a throttle roll-on. The Maico 501 or 1974 Kawasaki KX 450 being its only rivals there, that come to my mind anyhow.
