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47silver's Avatar
 
Join Date: Sep 2002
Location: Pittsburgh
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MFI idle bypass initial setting on a 1972 911T

I have read most if not all of the MFI information (i need an aspirin) but have a question that remains mysterious.
Lee Rice indicates that the idle mixture screws should be turned out 2.5 turns for bottom stop.
the porsche CMA document states that a 2.4 should be 3/2's which i believe means 1.5 turns from bottm stop.
The CMA differentiates the 2.4 from the 2.2 which has 2.5 turns from BS.
is Mr. Rice correct or should I use the CMA document to set up the idle bypass?

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Old 05-28-2019, 12:45 PM
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It doesn't matter as long as it starts, do the flow at 3,000 rpm as per the cma. If the idle is too low open them all equally to get to idle rpm. If too high close them all equally. If you do the adjustment properly at 3000, you probably will not have to move anything at idle.
Make sure your timing and dwell are spot on.
GO STEELERS!
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Old 05-28-2019, 02:46 PM
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I split the difference at 2 turns out when I set up the MFI on my 2.4. It doesn't really matter too much where you start, just make sure that the throttle stops and links are adjusted properly, and that all 6 bypass screws are backed out the same amount.

The initial setting is only a rough starting point. You will deviate from it when you check and adjust the vacuum on all six stacks.
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Last edited by Arne2; 05-28-2019 at 03:47 PM..
Old 05-28-2019, 02:48 PM
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The 2.5 turns is just a starting point . The most effective second step for me is to then take a tube and put it up to your ear , the other end just in the velocity stack and make note of how far it is into the stack. Listen to the sound , as you turn the screw in and out the sound will change . I listen for the loudest combo popping thumping . Practice and you can get all the runners sounding the same .
repete for all stacks
Just an old tune at the track trick .

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Old 05-28-2019, 02:51 PM
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