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Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.

1970 Yamaha XS650 Tune Up

Motorcycle Classics tech expert Keith Fellenstein

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Tune up

Q: I figured it was time to do a tune-up on my 1970 Yamaha XS650. I had a tune-up kit a friend gave me, purchased in 1981 at Seattle Yamaha, and the “How-To” article from the January/February 2011 Motorcycle Classics  in hand, proper tools and experience. I timed the right cylinder, lining up the “F” on the engine cover with the timing mark and tightened down the backing plate. When I went to time the left-hand cylinder, the timing mark was advanced (to the left of) the “F” and there was not enough movement in the half-plate to bring it back (it was up against the stops/screws). I left it with the right-hand cylinder properly timed on the “F” and the left, slightly advanced. Do you have any suggestions on how to correct the timing of the left cylinder? — Terry Zeri/Bellingham, Washington

A: There are a couple of ways you can pull the left cylinder into correct timing. You can go back to the right cylinder and close the points gap by a thousandth or two. That will have the effect of advancing the timing for that cylinder. Then you rotate the full plate to retard the timing enough to bring the right cylinder back to the correct setting. That may be enough to allow you to use the half plate to correct the left cylinder timing. If that doesn’t quite get it, you can then open the points gap on the left cylinder by a thousandth or two, which will have the effect of retarding the spark for that cylinder. If the left cylinder is not too far advanced you may just be able to open the gap as mentioned and have that correct the timing. Good luck! MC