Malfunctioning vacuum advance?

[John76]

1 hour ago, '76mintgrün'02 said:

These distributors were designed to work as part of the emissions package, so it may not be as simple as we'd like, trying to figure out how to make them work for us.

Yep...Trying to understand how/why BMW was addressing emission requirements with the different distributors, EGR and air pump combinations (or lack of) is an interesting study...to some at least (e.g., those with cars that still require smog stuff).

I have tried many combinations of vacuum advance/retard with manifold/ported/no vacuum sources, plus numerous timing settings, etc. I have settled on manifold vacuum advance for the following reasons: 1) Static advance near TDC provides better cold starting since the initial spark occurs at maximum compression (TDC). Note: There is no mechanical advance at cranking speed. 2) Once the engine has started, you get maximum vacuum advance (12 deg.) plus about 3-4 degrees of mechanical advance (at idle speed) and bit more at fast idle (when choke is on). This makes for a smooth idle. 3) Manifold vacuum drops out completely at WOT, but still gives you lots of advance at cruising speed (3500rpm @ 65mph) which gives you greater fuel economy. 4) The added manifold advance at idle/low speeds makes the engine run noticeably cooler.

My car runs soooo much better when I have manifold vacuum advance at all times, and NOT routed through the Black electro-valve, which shuts off the vac advance when the engine is warm.

Happy Thanksgiving! .... we are still friends...right?

John

['76mintgrün'02]

2 minutes ago, John76 said:

2) Once the engine has started, you  "I" get maximum vacuum advance (12 deg.) plus about 3-4 degrees of mechanical advance (at idle speed) and bit more at fast idle (when choke is on). This makes for a smooth idle.

 

"I" fixed that for you, my friend.

[jimk]

John,

But you live in Cali where they insist on all that funky equipment.

[MarcD]

Update time

 

After chasing a weird idle issue that I was blaming on timing turned out to be a MISSING secondary idle jet. Not sure how I missed it. I checked every vacuum line and port and still overlooked it. It wasn't until I went to change the jets that I noticed the holder and jet were gone. Strange. I'm honestly surprised it ran as well as it did.