BBI CSI question | FerrariChat

BBI CSI question

Discussion in 'Boxers/TR/M' started by bl10, Oct 13, 2025 at 6:48 PM.

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  1. bl10

    bl10 Formula Junior

    Jun 8, 2011
    444
    Chatsworth, CA
    Full Name:
    Barry Leavengood
    84 BBI Federalized and Ca BAR certified. G&K ECU, Frequency valve (1), narrow band O2 sensors (2) spliced together, WURs looped together via vacuum line, cats, MSD 6AL ignition with stock coil. 21K miles Passes CA smog with no problem.
    Acquired Jan 25 with 18K miles and it had several "drivability" issues. Have most issues resolved but a couple of things I don't understand about the CSI cold start and hot idle. When I first got it I had to set the hot idle at 1.7 K with air bleeds or it would continually stall when cold snapping (like taking foot off gas to shift) back to idle.
    To cure this I adjusted the Aux-air-valves(2) to full open when cold and balanced the system side to side with vacuum gauges and manometer. Also did some work on the distributor as the advance bushings were broken, thanks Eric Sander. Got it to where it idles hot at about 1250. (in car tach) and doesn't stall ever when cold. However it does surge when cold until it warms up.
    So thinking it should idle a little slower and not surge I took a long look at the throttle body butterfly stop screws and air bleeds.
    Turns out the throttle stop screws were a full 4 turns in and I had adjusted the air bleeds to about 1/2 turn out.
    After reading threads, thanks Rifledriver, the suggested settings are the throttle blades set at 3 thou or about 1/4 to 1/2 turn in and the air bleeds about 3 turns out.
    So I disconnected the linkage and set the stops at 1/2 turns and air bleeds at three turns.
    Hot idle speed increased to 1500 so I backed the stops to 1/3 turns and closed the bleeds to 2 1/4 turns and rebalanced.
    Now idles at 1100 (AC off) and doesn't surge or stall. Much better.
    So after that lengthily explanation my question is a simple one .

    Is the primary purpose of setting the throttle body butterflys open such a small amount is so they won't bind or jam in the throttle body when closed rather than setting idle rpm and the air bleeds are used set idle rpm? The way its currently set it won't idle with the air bleeds closed.
    One other thing. Apparently there is no dash pot to slow return to idle?
    Thanks for your patience.
    Barry
     
  2. carguy

    carguy F1 Rookie

    Oct 30, 2002
    3,428
    Alabama (was Mich.)
    Full Name:
    Jeff
    It's been a L-O-N-G time since I've fiddled with CIS. Yes...you are correct, the throttle valves are set so no binding or wearing into the the plenum over time. The air bypass screws are for setting idle speed. The mixture adjustments can also play a role in idle speed.
     
  3. bl10

    bl10 Formula Junior

    Jun 8, 2011
    444
    Chatsworth, CA
    Full Name:
    Barry Leavengood
    Carguy. Thanks so much. That was my conclusion. I haven't messed with the mixture yet as I'm not sure of the interplay between the frequency valve and mixture. In other words would the o2 sensors / ECU / frequency valve override the mixture adjustment. If I get a chance I'll add a couple of wide band O2 sensors so I can monitor the changes.
    Thanks again
    Barry
     

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