Points problems

[lrz]

Gents-


'77 100/7

ran like a top last Fall, properly stored with non-ethanol gas in December.
Installed known good battery a few weeks ago, full choke, and the motor sprang to life within a few seconds as always.
A few hundred miles later, on the third or fourth ride, there was a bit of hesitation/stumbling.

On the next ride, the wires from the clutch switch broke; this turned out to be a red herring, but I could not get the motor to start using the thumb switch, regardless of gear selection or clutch engagement.
All lights were on, just no juice when switch was depressed.
Had to bump start it at that point.
Removed the starter relay, cleaned up the contacts and the motor fired readily using the thumb switch. No problem since.
On the last ride, the motor quit several times though it did restart semi-willingly; there was one loud 'backfire' on the last restart before I made it home.


En route, my first thought was that my tank bag was not allowing the tank to vent, though I've used it for years, so I cracked the gas cap resulting in minimal if any change.

I checked valve lash which was .10/.20, spark was blue/purple, NGK plugs new last summer.

Then I began to think about the points which I haven't paid any attention to for at least 5 years and ??miles.
The contacts themselves looked essentially new.
But, when I last timed the ignition it was necessary to enlarge the holes in the plate in order to more fully 'retard' ignition by turning clockwise.(I believe this advice came from Duane's site..?)
It has run well ever since w/ "F" centered in the window as per inductive timing light.

No matter what I did this morning, using a point gap of .016 ( really everywhere from .014 to .020), the points would be open with "S" showing in the window.

So, I swapped out the entire ignition sensor assembly with a used one, excepting the ATU though I do have a spare.
Gapped points .015 and static timing was close.

The motor fired a bit hesitantly; at full advance the "F" was high and, as before, the exchanged points plate also required turning to full clockwise limit, though these holes have not been enlarged, at which point the "F" was centered @ 3500 rpms.

Of course the motor was now warm, but it did/does fire easily.
However, I wonder if something else is just not right.

The question-

why does this motor require full 'retardation' of the ignition timing to run well?

Or am I doing something massively wrong?!?



Please- I'd prefer to confine this to my current scenario and not stray into the electronic vs points debate.

[Major Softie]

Timing chain jumped?

[lrz]

Interesting thought.

Wouldn't that be unlikely unless there was extensive wear?

However, timing chain/gears installed off by a tooth or so..?

[bbelk]

A super worn timing chain can require a little file work on the points plate to get the timing right.

[Seth]

Try replacing the condenser. I had this problem a couple years ago with an r90s. It would start and run for a while. Then it would start to miss and eventually stop running altogether.

[lrz]

Swapped as part of the assembly.


Interestingly, maxbmw is out of points.

[Bamboo812]

Try putting the old condenser back in. They rarely fail, but it is not unheard of for a new one to be faulty.

[SteveD]

Swapped as part of the assembly.
Interestingly, maxbmw is out of points.

Pointless post!