Personally I have never taken efforts to measure throttle cable slack.  I set it so the cables are loose enough the carbs are at idle and there is no change in RPM when turning the handle bars.   LOL, I suppose I could manage to measure things.

Again, this luckily is a simple thing to check, perhaps that is the problem?   St.

  I have been following this topic since the start. I wonder about the slide(s) underneath the diaphragms. More specificly, the needles and needle jets. These are wear parts. The grooves that hold the needles in position at the top of the needles, inside the slides, can get worn and not hold the needle tightly in place. It seems to me that if the fit of these parts are worn, could there be a tiny bit of a bind when transitioning from acceleration to deceleration. File this post in the wild ass guess category.

James, that is a good point to bring up and one I had forgotten.   Also, are there springs inside the carbs to return the slides to the closed position?  I don't know R65 carbs to know for sure.  Perhaps a spring is shot?   St.

Boy, you have got a “ tiger by the tail”, as they used to say.  Keep us posted, for sure.

I gotta say, I still don’t like the BLURRY bit.  The image of your timing marks, and the teeth on the flywheel, should be clear.  And, when you slowly raise the throttle, the image should smoothly “rotate” from the S mark to the F mark at 3500 rpm or so.  Then, the reverse on the way down.  The older bikes with open points routinely had a “double image” with the timing light, because of a slight imperfection of timing between the cylinders (each 180 degrees of camshaft rotation).  I would think the “points in a can” upgrade would have eliminated the double image issue.  However, even with the double image, it was not blurry, it was clearly a double image; like two S marks overlapping.  Now that you have overhauled the bean can, I would still get a known good bright timing light and verify that the ignition is firing and advancing, and retarding, in smooth fashion.  That’s my thinking.  Just to put that to bed.

Mr. Strickland’s wild-ass-guess hits close to home.  I chased an issue for years that felt like a slight lean surge in the midrange.  I finally found that it was indeed one on the slides (Bing says piston) in the CV carb.  It had a sharp burr or edge at the top of the central steel tube.  Picture attached.  It caused the slide to hang a bit, and produced this strange drivability issue.

I've always suspected the carbs, but I've rebuilt them a couple of times with Bing's more complete kit, which includes the needle and jet. She has the flat-top 32mm carbs, which the old-timers said were inferior, but I've never understood why. There's no spring in the slide assembly, which I believe the dome-top models do have. Is that why they are inferior? The slide is just a rather heavy cylinder that goes up and down due to pressure differential between two pressure areas, the boundary of which is at the diaphragms. The needles are held at the bottom of the slides. I've experimented with the needle positions. They clip further up or down. The service guy at Bing talked me through checking the idle circuits. Other than that I can send them to him. Maybe he will find something wrong that nobody has thought of.

I recall the spline teeth at the final drive looking somewhat worn last time I changed the tire. I don't know how worn is too worn. Should I take the wheel off and take a picture of that?

I’m not too familiar with the flat top bings. I’m sure they are fine. I don’t think they have the central steel guide tube in the picture I posted, right?  I also had rebuilt my carbs several times, and played with needle jets, idle jets, needle position, you name it. It wasn’t until I was very carefully checking the free motion of the slide in the cap, with the parts in my hands, that I detected the problem. If I applied a slight lateral force on the slide, it would grab instead of moving smoothly. It was the sharp edge I mentioned. Hardly detectable, but it it was enough to hamper the smooth motion of the slide. I was so glad to resolve that issue!  If a slide were to hang, and then let go, it would make for lurchy driving. 

PS:  I too had several consultations with the Bing man. When I told him what I had found, and that it fixed my problem, he said he had never encountered that particular issue. There ya go, always room for a new glitch.  My theory is that the slide was once dropped or knocked off my work bench at a school where I worked. 

David,

Right, my flat-tops don't have the  smaller-diameter cylinder on top of the piston. What does that do, anyway? Are our carbs the same except for that? By the way, look at my avatar if I have loaded it correctly. You may see a similarity with your bike fairing-wise.

LOL, Let me clarify myself.   Since I can't see what the owner sees, I perhaps misinterpreted "blurry" of the timing marks.  I meant double.   I don't know the quality of the timing light used.  

Lots of good ideas coming out of the knowledge base here, good luck. St.

I can hardly believe you have a Hannigan, and your bike is yellow!  If we ever pass each other on the road, it will be like all the planets aligning during a solar eclipse. 

@4949 I've never seen another Hannigan on the road, much less a yellow one! Where are you located. I'm near Seattle.

These rear drive teeth are, I think, very worn. Depends on what they are supposed to look like. Could this be the cause?

@stephen-ladd We retired in 2017 and moved to the very bottom of Texas (Mission, TX). Prior to that we lived in Kentucky since 1989. In 1991 I was managing a project at a new Boeing plant in Auburn. Was out there for about 18 mos.  Had my bike with me. Picture attached with Mt Hood in the background.

I think your wheel drive spline is about 50% gone. It’ll still go for a while, but you will have to get it restored long term. personally, I wouldn’t want to push it past 2/3 gone. 

I went back and read your initial post. So, this has been a developing issue for a long, long time. Interesting. Tomorrow I am going to check my total drivetrain “free play” at the rear wheel, like you did, and report back to you. 

On the drive spline, if you look at the very bottom of the pocket, you might see a sort of step that would be an indicator of the spline wear relative to new. I'd go along with the 50% assessment. The drive spline on my R75/5 is just about the same. My bike does not buck, however if you apply acceleration just right while coasting, it makes a pronounced banging noise.