Timing question

[MikeC23]

I come for sage like advice! I am tuning up the bike in case it ever stops snowing in Western PA. Cam chain. Check. Valves. Check. Timing. Aaahh. We have a problem. After gapping the points, the right cylinder was dead on. The left, however, is too advanced. The plate under the points is already rotated as far counter clockwise as possible. Any suggestions for retarding the timing on this cylinder?

 

[650Skull]

Have you checked the cam Chain tension ..............if they get over stretched the points plate cannot be set properly

 

[MikeC23]

Yeah. I set mine while the engine was cold as per the manual. Someone suggested I do it after warming the engine, which I will do tonight.

 

[5twins]

The lower set of points for the left cylinder mount on a smaller "half" plate on top of the main backing plate. You've moved that half plate as far as it will go? If so, then the only other adjustment you could play with would be the points gap. Changing that will change the timing too. Make it smaller to retard the timing.

 

[MikeC23]

Yep.Both plates have been rotated completely counter-clockwise. If I set my gap at .014 iniatilly, how far down should I go? .010? or even .09

 

[5twins]

I think the minimum setting is .012", but if your points are used and slightly pitted, the gap you're measuring isn't the gap you are actually getting. The spark jumps between the pits so the gap is actually bigger than what you measured. I'd say if you have to go down to .010", do it.

Also, besides the rotation on the points plate, sometimes there's a little side to side or up and down play in it. That can throw the timing off too. In your case, the rubbing block for the lower left cylinder set of points is on the left, at about 9 o'clock. Try moving the backing plate or half plate that way, towards the left, to retard the timing more.

Running out of timing plate adjustment is one of the symptoms of a stretched out timing chain. How many miles are on the bike and have you ever replaced the timing chain?

 

[MikeC23]

Does a stretched cam chain advance or retard the timing? Or can it do one or the other? It has 22k on it. I haven't replaced the chain, personally, and I'm not sure if the PO did either. It was on my short list for this winter but there's no heat in my garage and things got cold here in western PA. I'm putting some thought into buying a second motor, working on it all summer, then swapping them out. Since they're so cheap, I ordered a new set of points to see if that helps. If not, cam chain changing time it is! Thanks for the advice.

 

[5twins]

Well wait, now that I think about it, I'm pretty sure a stretched chain retards the timing, so maybe that's not your issue. Yes, try new points. Sometimes an old set is worn so much, you just can't get it set correctly anymore.

But, by 22K, many original cam chains are pretty stretched out. They certainly can and do last much longer in some cases, if they're properly cared for (adjusted correctly and frequently enough). That's the thing, most never were. There can also be an issue with the '76-'78 (and some '79s) type D cam chain adjuster. It didn't have a lock nut on it for the adjuster screw. The acorn cover nut acted as the lock nut. The problem is, when you tighten it down, it can tighten the adjuster more along with it. Then you end up with a chain set too tight and that can lead to premature stretching.

 

[MikeC23]

Fortunately, mine has a lock nut! I keep pretty close tabs on this thing since it's my baby. Depending on how many miles I'm riding, I generally check things about once a month through the summer.

 

[Thomas]

Had this lack of adjustment problem on a backplate with new points.Yamaha had at least two different types of points and are not interchangeable. I dug up another set of points and all was well.

 

[TwoManyXS1Bs]

Had this lack of adjustment problem on a backplate with new points.Yamaha had at least two different types of points and are not interchangeable. I dug up another set of points and all was well.

Interesting, not interchangeable? Here's a good read:

http://www.xs650.com/threads/different-set-of-points.51146/

 

[Thomas]

I stand corrected! I was tired of reading about cam chain stretch when the problem was more likely points/backing plate,

 

[MikeC23]

New points installed and BOOM! Timing is dead on!

 

[5twins]

Well, good for you. Mark down your mileage. Points should be replaced about every 10 to 15K miles, even if they still look OK. They are a wear item. The faces get worn and pitted, the rubbing block wears away, and the spring steel strap that snaps them closed can get weak. That last item is a biggie. There's no way to fix that other than replacement. I had to replace some points on a local guy's 650 because of that. I told him several years before that, when he first got the bike, that he should put new points in because he had no idea how old or how many miles were on the ones in there. He never did. Eventually, the bike just up and quit running, lol. The spring straps wouldn't close the points tight enough anymore to make good contact when closed. That meant no charging up of the coil for the next spark. With new points installed, the bike fired right up with less than one kick. That's right, less than a full kick. It was running before I had kicked it fully through the kicker's stroke.

 

[MikeC23]

That was part of what was wrong with mine. The springs were REALLY weak and, I never noticed this before, but they were two completely different styles of points. Sometimes I really wonder what the PO was thinking with this bike.

 

[5twins]

That incorrect point set was most likely the problem. It's rubbing block probably didn't contact the points cam in the same spot as a correct set would. That would change when the point set opened, in effect, change the timing. Apparently, the amount of adjustment available on the point plate wasn't enough to compensate for this.