E: Engine Auto advance unit tabs - should there be four?

[CoreyL]

I was riding my B Meteor yesterday and, for 40 miles, it ran flawlessly. I had been rolling along at 55 mph and was cresting a slight rise (one I had crested many times before) and the engine started to lose power. It didn't seem to want to go faster than 40-45 mph. I was afraid I wasn't going to get home or that, if I had to stop at a traffic signal, it would stall and not restart. I did have to stop at a few lights and it idled fine and pulled away from the lights as normal. I made it home (about 10 miles) and the bike seemed to behave normally under acceleration. I was on city streets and didn't have an opportunity to take it back up to 55 mph.

When the loss of power happened, I opened the second petcock and opened the full cap - neither action had any effect.

This morning, I pulled the plug (KLG FE75) which looked fine. I checked compression, which was normal. I removed the cover over the auto advance unit and the bob weights seemed to move freely. I did notice that one of the tabs that limit movement of the weights was missing (see photo). However, one of the remaining tabs still seemed to be doing the job of limiting the movement of the bob weights. Also, looking at the movement of the weights, it looked like the missing tab, had it been present, would've prevented the weight from making its full range of motion.

I also removed the float bowl on the Amal concentric carb and took a look around. No grit in the bowl or blocking the jets.

Any comments/thoughts/advice about the loss of power or missing tab would be appreciated.

 

[LoneStar]

One pair of stops should still be effective, as the moving center is a single part. But as you suggest, the now-missing tab may have been the one actually limiting the range, so the timing may have altered. The farthest tab clockwise of each pair limits full advance, so your missing one could result in greater full advance if it had been limiting the motion.

Still, the tab pairs should be matched in range so only a small effect. And it's not clear how a bit more advance would explain the engine's behavior at speed. Might be wise to check the timing in any case; the ATD might have slipped on the armature shaft. And is the missing tab bouncing around in the timing chest?

 

[Sten Jensen]

Beware, two of the stops are weakened by the spindle hole bored through the plate just at the point where it is bend.
And the timing side does not like a stop passing through the gears,,, on my Comet it broke the thread of the large idler spindle and loosened the spindle in the old alu. boss.
With only one stop left it has to cope with double force.

 

[Alyson]

The big deal is "Where is the missing tab ?" You should be thinking of opening up the timing chest to make sure it's not floating around in there. Hopefully it doesn't go too far. Hopefully.

 

[Peter Holmes]

What has happened to hexagon headed bolt, was it a rev counter drive? I would also be worried as to where the missing stop has gone, it is a significant lump of metal, if it had gone between the timing chest gears I think you would have known about it, certainly a bit more than a power loss.

 

[Sten Jensen]

If a Rev. Counter is driven from the center it will try to retard the ignition, especially if the cable is seizing. That might explain the power loss.

 

[CoreyL]

If a Rev. Counter is driven from the center it will try to retard the ignition, especially if the cable is seizing. That might explain the power loss.

The bike doesn't have a rev counter.

 

[Jim Richardson]

Sorry to highjack your thread, but I was about to ask if it’s possible to remove the centre bolt from the assembly easily and it seems you can, How ?

 

[CoreyL]

The big deal is "Where is the missing tab ?" You should be thinking of opening up the timing chest to make sure it's not floating around in there. Hopefully it doesn't go too far. Hopefully.

Popped off the timing cover and the broken tab was sitting at the bottom. No apparent harm done. However, it looks like the broken tab had been making contact with a boss inside the timing cover. See attached pics. No idea how long it was making contact before it let go. Also, no idea how it got bent enough to contact the outer case.