Vacuum retard

T.Hanson · Post by **T.Hanson** » Fri Jul 24, 2009 9:24 pm

'81 528i : the vacuum retard port (tube) under the throttle body is plugged with a red rubber cap. I assume the small tube under the distributor for vacuum retard is left alone, no plug necessary, as it came off without anything there.

What happens if I unplug and put a vacuum tube to the distributor ? The serial numbers matched between old and cleaned version but are some distributors made to not vacuum retard ?

Mike W. · Post by **Mike W.** » Sat Jul 25, 2009 12:46 pm

If the distributor has the same number on it and has a vacuum box on it, I'd say it's safe to use the retard function. What would happen? The idle speed would go down.

T.Hanson · Post by **T.Hanson** » Sat Jul 25, 2009 4:05 pm

Terminology: The distributor has a round pot on the side with a top and bottom vacuum fitting. Is that the box you are referring to ?

All three distributors I have are like that. The '81 simply has the throttle body (lower ) vacuum fitting capped, and the lower distributor tube is just there.

I'm not a fan of 800 rpm idle, preferring 1000. To get there I open the big brass throttle body screw. Seems fine on the '81 with the valve cover aux air but the '79 with the Nemo (probably dirty) likes to zoom/drop until warm if I do that.

Mike W. · Post by **Mike W.** » Sun Jul 26, 2009 12:22 pm

T.Hanson wrote:Terminology: The distributor has a round pot on the side with a top and bottom vacuum fitting. Is that the box you are referring to ?

Yes.

All three distributors I have are like that. The '81 simply has the throttle body (lower ) vacuum fitting capped, and the lower distributor tube is just there.

I'm not a fan of 800 rpm idle, preferring 1000. To get there I open the big brass throttle body screw. Seems fine on the '81 with the valve cover aux air but the '79 with the Nemo (probably dirty) likes to zoom/drop until warm if I do that.

Too much advance will cause that, but if you can put up with a high idle during warm up, just pulling a wire off the idle switch on the throttle body will eliminate the surging, and with no other symptoms I've ever found. Or if the 79 doesn't have vacuum retard hooked up it will definitely do it.