Posted: Fri Nov 17, 2017 12:44 pm Post subject: Adjusting the timing on a CT90
I was working in my shop and decided to document in a post on my blog the process I follow when I adjust the timing on one of my CT90's and I thought I would share the link below in case it was useful to others.
Joined: Jul 08, 2014 Posts: 873 Location: Vacaville, CA
Posted: Fri Nov 17, 2017 2:03 pm Post subject:
Mike, excellent and thorough explanations as usual. Just one suggestion, when setting the points gap I did not see where you stated first making sure the points rubbing block was on the highest point of the advancer cam - or maybe I just missed it. Your photo does show the rubbing block lined up with the two notches on the cam though. Another nit picky thing is if there is clearance between the points plate and the housing, the points gap can change when rotating the plate to set timing. Snugging up the fit using a sharp center punch on the aluminum housing adjacent to the plate in a couple of spots will solve that problem.
It might also be worthwhile emphasizing the need to make sure the points contacts are free of oil by spraying with contact cleaner, and by wiping down the feeler gauge first with cleaner.
And a couple of quibbles: I'm skeptical of the statement that a big bore kit would require more advanced timing. Timing specs generally fall within a similar range for similar engines regardless of displacement. And even if there were some advantage to straying from factory specs, how would anyone test that sort of extensive dynamometer work? I remember back in the 1960s a friend set up a way to vary the ignition timing on his Honda S90 using a screw and knurled nut system he could adjust while riding. He went out on a flat road and ran full throttle while varying the timing from retarded to very advanced from stock specs. It turned out he could not detect any difference in top speed. He also tested acceleration between two road markers and found no difference in speed at the end of the distance.
Also, a worn cam chain will retard valve timing, but since ignition timing is adjusted in relation to crankshaft position, not cam position, there is no need to set the timing more advanced from stock specs due to a worn chain. The act of setting the timing already takes any chain wear into account.
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