Early MFI questions

Some may remember my question about my car idling too high, spoke with a knowledgable mechanic that has done work on my car, and he proposed that my stacks/butterflies may be worn and leaky. As the engine heats up, the stacks expand and slowly leak more air, which makes the idle slow climb from set idle to around 1500-1600 rpm (when he worked on it he set it to around 1100 rpm).

Question:
1. Do you guys think I could set the base idle low (i.e. around 700-800 rpm) and as the car warms up and the stacks "leak" it would settle at a lower rpm?

2. What is the proper method for adjusting the idle down? Is it as simple as adjusting the idle mixture screw on the MFI pump or is it more involved? (I have the Bosch adjustment tools on order)

I'm trying to learn as much as possible about adjusting the MFI and do things as correctly as possible, although after reading the Bosch manual, I think that is a bit too procedural and involved for this adjustment (and i don't have a dyno to measure emissions )

TIA,

Brad

There are a few things involved in trying to get mfi to work properly. I will only touch base on the idle issue. If don't have a carb synch-buy one. You can purchase them at pelican. There is a cheap one that is around $40.00. It lays on top of the stack. You have to position it just right. There is a better one that fits into the stack. It produces a tight seal. It is around $70.00. There are 6 screws located each at the base of the stacks. Turn in to lower and out to increase. There are 2 adjustments on the front of the pump. A bottom end adj. and a top end adj. The top end adj, does the most in the sense of idle fluctuation. It is located behind an allen screw on the front of the pump towards the top. unscrew it and insert a very thin screwdriver. Turn ever so slowly until you feel it grab. turn it in to lean pump out which will also lower the idle and visa versa. There are allot of other things involved in getting this right. I.E. timing. tuned engine-valve adj.etc.. These should all be done first before you start messing with the pump. Also check and see if the pump is timed corectley.There is a mark on the back of the pump that has to line up with a mark on the pully on the back of the pump. These marks also coincide with a mark on the front pully called FI. Line them all up and the pump is timed.
I'm sure someone will also give you much more on this subject.
cheers

Brad,

I would strongly recommend doing some extensive reading at this Pelican page:

http://www.pelicanparts.com/techarticles/911_MFI/TipMFI.htm

Most are important enough to read, but ultimately, the Check, Measure and Adjust document by the factory (also known as the Blue Book) is the important one, and should be followed carefully!

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Warren Hall
1973 911S Targa

often the balls and sockets are quite worn and one or more stacks won't return to idle. a couple of homemade brackets and return springs on the #1 and #4 stacks often work wonders to pull each set of three closed. not the best fix, but effective.

[This message has been edited by john walker's workshop (edited 05-04-2001).]

Thanks all for the great info! Has anyone had their stacks rebuilt? I'm trying to find a good shop to do it for a reasonable price (err I know *reasonable* is always a relative thing when it comes to these cars )

Brad

eurometrix 408.296.1533.