XS11 Off Idle Stumble

[DEEBS11]

How easily does it start when warm? If it struggles, I would add float valve o’ring leak to your list.

Marty, it actually starts very easily at any temperature. Mind boggling.

[DEEBS11]

Here is an update: Wrenched on it all day. Here is what I tried/found:

Checked all voltages including every pin on the TCI and coils. All normal 12V. 13V-14V while running.

Compression check - All 4 cylinders within 5 PSI.

Tried a set of known good used plugs. No change.

Removed and serviced carb floats. Cleaned seats with polish. Checked fuel level in all 4 carb bowls. No change.

Installed a mint 1980 advance unit with only 18K original miles. No change.

I can only draw two last conclusions. A weak coil or the cam jumped time. However, the engine runs smooth (internally) no weird metallic noises.

[DEEBS11]

Spare Advance unit. No change.

[DiverRay]

That is just the vacuum advance unit. Did you service the mechanical advance that lives behind that? If you have a little rust on the weight fulcrum points, it may cause a lag.

[DEEBS11]

Good point Ray, It is clean, well lubricated, and works perfectly.

[bikerphil]

Sometimes those brass vacuum ports on the intake manifold boots can work themselves loose and leak. Don't know if you checked those.