Just another thought, when you changed your rear tire, what condition was the final drive spine and dog in?  I have had to replace mine twice in 200K plus miles.   Wear can be faster if you do a lot of up and down shifting.  St.

Posted by: @joe-hall

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Just wondering, at 170,000 miles, have you ever changed the timing chain? 

And you don't R&R the timing chain without installing the updated tensioner spring at the same time. 

I have replaced the diaphrams a couple times. I know what it's like when one of them goes out.

I have had diaphragms develop holes, so I have first hand knowledge of that, I can't say I have first hand knowledge of what happens when they just get stretched and old.   As a cheaper part, maybe replace them?

Two other things sprung to mind.  What is the condition of the gears in your twist grip?  Is it well lubricated inside?  Check for vacuum leaks in the carbs and the mount into the head.  Easy to do, spray carb cleaner, or something around the outside of the carbs especially near the butterfly valve shaft and the header between the carb and head.  An increase in idle means a leak.  Butterfly shaft o-rings or seals are known to go bad and to be honest replacing them can be a pain. They sometimes get left out of the carb rebuild loop.   St.

I’ve never owned a “points in can” model, but I would think that if the advance is sticking/malfunctioning, you could SEE it using a timing light. Peering in the timing window with a timing light, and slowly bringing the rev’s up, and down, you SHOULD see a smooth transition from the S to the F mark.  If the advance is sticking, the transitions would be jumpy.  You will see it being jumpy, watching the timing marks and the starter teeth on the flywheel.  It will be evident. 

I had an electronic ignition act up with advance problems. A. It made the bike buck, and B. I could see it clearly with a timing light. 

Hey David, funny you should mention this test, I have been emailing Stephen and did suggest what you write about.  Good tip, thanks for sharing. St.

So you all know, the consensus pointed to either the advance mechanism getting sticky (for that I will soon be taking apart the "bean can", lubing it, and putting in new springs) or something in the drive train such as the drive shaft coupling or the final drive. I will do the advance mechanism first because with so many miles it should probably be done anyway. If it doesn't help, maybe this winter I will take apart everything aft of the transmission and look for wear in there.

I tried looking for advance mechanism stickiness with a timing light but it's all too blurry. Don't know if that is another bike problem or a cheap timing light.

Add another possible thing to the list.  When you last replaced throttle cables, were the marks on the twist grip and gear lined up?  One tooth off can cause throttle open and close issues.  St.

“All too blurry” seems suspicious. Should have a clear image. I’d sure try another light, if you think yours might be bad. Or try your light on another bike or car. Kinda betting you are going to find the problem in the bean can. Keep us posted. 

Posted by: @4949

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“All too blurry” seems suspicious. Should have a clear image. I’d sure try another light, if you think yours might be bad. Or try your light on another bike or car. Kinda betting you are going to find the problem in the bean can. Keep us posted.

One reason you should use a strobe light is to have a visual indication of exactly what's going on with the ignition timing. The "blurry" factor is not an issue with the light, but rather an indication that the mechanical advance is completely worn out. "Blurry" comes from the fact that the ignition is firing at a different time on each engine revolution. One time advanced, the next time retarded, the following time in yet a different location. To the human eye, the final picture of the timing marks is jumping all over the place, or what we call "blurry". 

And the "blurry" will not go away until the ignition timing becomes stable and rock solid again. The "blurry" is merely the total sum of ALL the mechanical auto advance springs, pivot point fits, ignition cam fit, etc being completely worn out after nearly a half-century of service. 

So your machine is (visually) telling you one of the things that's wrong with it. All you need to do is "listen". 

I don't have the bike to "see" what the fellow is talking about in terms of blurry, Points equipped bikes alway have some degree of blur with a timing light, even my electronic ignition bikes have a bit of blur.  A LOT of blur is abnormal. LOL normal blur may be abnormal to someone else.    

As this is a points in a can bike, the advance mechanism is holed up in the can and not readily accessible.  The owner is going to do what he can to assess the condition of the advance system.   He also has a long list of other items to check as well.  

I am starting to think the advance system is a non issue.  From what I read, the timing mark advances and retards with throttle.  I would consider a sticking unit IF, when the throttle is cut the timing mark stayed advanced or was slow to return.  

Time will tell.  St.

This is an update on my roll-on/roll-off bucking problem. I rebuilt my “points in a can!” Thanks to the info via Steven Rankin - I can provide the link if anyone wants it. The can came apart with difficulty - hammering on the shaft from back to front. Lots of crinkly black dust fell out. Any grease had disappeared. Cleaned, greased, installed new springs and O-ring (Euro Moto Electric), replaced the cannister, re-set points and timing. (I am now using a dwell meter, not just setting the points gap. I’m feeling very scientific!) All this has seemed very much worth doing. The marks are now less blurry in the timing light. I feel it is advancing smoothly. But it has not affected the bucking! My bike now hauls ass, but then it always did. My points ignition system has never been finicky. Whatever adjusting I do it runs equally great. Except for the bucking, which is an annoyance at low speeds, like stop-and-go traffic. I will continue with other suggested fixes over the winter.

Well, one off the list and thanks for the follow up.  Next relatively quick check is the marks on the twist grip, when you changed the cables are you sure you lined them up?  Second would be the final drive splines.   St.

I don't think I could have failed to install the throttle cables correctly, I've done that many times. 

Here is a clue worth emphasizing. The power kick-in has no sound or feeling of metallic impact yet it is very sudden and instantaneous. I keep a couple mm's of slack in the throttle cables, measured at the ferrules on the carbs. The surge occurs when that slack is taken up. Likewise the reverse feeling when I close the throttle.