Motorcycle Classics Blogs > Tech Corner

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

welshman
12/18/2014 7:09:33 PM

Wideload gives correct sequence, but, advance springs are often weak causing points cam to be in different positions when static timing motor. Get new springs and check through rod is greased. It's also a good idea to check at full advance with timing light


chrisb
12/4/2014 11:32:25 PM

i seem to remember this happning on my 75 xs- think the advance weights were stuck, cant remmember,theyre at the opposite end of the cam? and drive the points on a shaft thru the center of the camshaft


wideload
12/4/2014 10:42:21 AM

Terry...I experienced this on two of my XS650s. Best practice is to adjust the cam chain tension, valve clearance and points, in that order. You probably already know that the point gap spec is .012 to .016. Like Keith suggests, I found that setting the gap for the right cylinder to the minimum provided the ability to (just barely) set the second set of points within spec. It's important to final check full advance with a timing light.