About 5 years ago I started the hunt for a 1970 Xs1 650 Yamaha. This was Yamaha's first 4 stroke motor after having built a reputation for fine 2 stokes. Honda threw down the gaulet with the 750 4 cylinder in 1969. The bean counters at Yamaha looked on the show room floor and knew something had to be done. The story has it Yamaha discovered a " Horex " engine design in their system from a company purchase years prior. They improved the Horex system and produced the 653 CC OHC and then stuffed into a frame that left a little to be desired. Drums brakes on both ends and no electric foot. Electric start and a disc brake didn't make the scene until the 1972 Xs2 model. The 1970 and 1971 motors were very snappy but for reasons that haven't been explained they de-tuned the motor in 1972. Popular Cycling magazine use to do 24 hour road test on bikes. They tested, flogged, the 1970 for 24 hrs (1191 miles) dropping it in the middle of the night and it never missed a beat and used no oil.
I found my project from a 650 chat line. A guy near Denver, Co. purchased one new and had a factory 750 kit installed. He rode the bike and then kids and family life moved the bike inder a tarp in the garage where is sat for nearly 25 years. I called and got the usual " ran when I parked it " story. He was asking $1,500.oo. I told him I had to be able to tell my buddies that I beat the asking price down and would he take...$1495.oo. Next day the check was sent and I called a old Army buddy who lived in Kansas. He picked up the bike and 3 weeks later took it to St Louis, Mo where his son was attending school. A week later I did a overnight and got the bike.
Once the bike was in my drive way I drained the carbs, cleaned the tank and changed the oil. It started after about six kicks. I rode the bike for year to determine it's needs. You really appreciate electric start and disc brakes after riding a 1970 Xs1. The last day I rode it the motor did not sound good. Later we discovered that early production motors used needle bearings in the con-rod. The left needle cage failed and scorned the rod. We also found that the lower engine case had been cracked. Someone used half a tube of silicone sealant to seal (hide..?) the damage.
A crank from a 1973 Xs 650 was installed and the motor was returned to the stock 653 bore. The crack was welded. With Mark Tomlinson's assistance we painted the frame and the body work. (Mark also helped with the motor work). Many parts were sent out for chrome and many more hours were spent watching Ebay for NOS or better then what I have parts.
To date the motor is in the frame and both wheels are keeping the frame off the ground. Next the carbs get rebuilt. Once that's done I'll fire the bike and hope there are no engine issues and it charges. If there are none I'll hang all of the newly painted body work and add it to the stable.
Mike Blackburn's 1970 Yamaha Xs1 650 Project