Micro-switch on rear carb QPIII...? | FerrariChat
Buy

Micro-switch on rear carb QPIII...?

Discussion in 'Maserati' started by F456M, Feb 5, 2014.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. F456M

    F456M F1 Rookie

    Jan 8, 2010
    3,696
    Oslo
    Full Name:
    Erik
    #1 F456M, Feb 5, 2014
    Hello experts. I have just bought a new Quattroporte III. Standard european version with automatic transmission. The car has not been used in many years.

    There are (on all. QP 3s I believe), a small micro switch on the throttle arm on the aft carburator. When this is depressed (throttles in fully idle position), a small valve is opened, and the vacuum in the manifold is applied to a vacuum diaphragm actuator on the distributor, causing the timing to be RETARDED. How is this supposed to work? Anyone here that really know this?

    It was adjusted so that it were never depressed. That can not be right, so I adjusted it so that it is depressed when the throttle is on the zero position. But because of the timing being retarded, the engine slowers to a stop. To make it still be able to run, I re-adjusted the carb linkage stops so the carbs give a little more gas (opening). But what happens now, is that if the car is idling for 10+ minutes, the exhaust manifolds turn both red hot..... But never when driving. Is the system working correctly, but the distributor timing wrong?

    I wonder what the reason is for having this system... Is it likewhen stationary in D or R the reduction of the revolutions will reduce the vacuum an this will lead to a bit less timing retard (more advance) to re-gain a bit more idle power so the engine will not stall?

    The engine also seem to have a about 50-70 hp less than normal.that is why I am thinking not enough timing advance. (Which will lead to too much retarded idle advance which turns the exhaust red hot. (I assume the valves get hot aswell...?)


    Please help me! Thanks a lot. Nobody seems to know how this system really works.

    Erik :)
     
  2. staatsof

    staatsof Nine Time F1 World Champ
    Silver Subscribed

    Mar 13, 2005
    96,022
    Fuggetaboutitland
    Full Name:
    Bob
    #2 staatsof, Feb 5, 2014
    Last edited by a moderator: Sep 7, 2017
    Try this thread starting at about message # 696

    http://www.ferrarichat.com/forum/maserati/328560-quattroporte-iii-catch-all-thread-35.html

    I believe it's covered in the QIII service manual (there's a link in that thread for a pdf version of that) though I've never looked to see.

    But yes, it's supposed to retard the timing at idle and then just off idle the switch causes the vacuum to bleed off and the timing advances. This system was first utilized on the later 1970's GT cars as a part of the emissions system I have it on my Bora.

    Were I you I'd disconnect it.
    Block off any air injection.
    Eliminate the catalytic muffler.
    Have the distributor modified to recurve the advance for best performance and full range.
    Check the cam timing.
    Re-jet the carbs.

    If local regulations prohibit this then you could just disable the switch and time the ignition normally but the advance curve is not optimal. Then you will eliminate that annoying just off idle surge. You could also check the cam timing.

    Then tune the engine.

    Maserati did not have it's act together when it came to emissions systems back then.
    You can burn the car up if operated as directed.

    This system was initially used with thermal reactors as were on my Bora. On cars of that era there is a plaque in the engine compartment warning that the vehicle is not to be sold in areas above 4000ft in elevation. The mixture gets too rich and they turn into blast furnaces. Ask me how I know?

    There's a very low milage 77 Bora on eBay at the moment. One of it's pictures shows that plaque.

    If you leave the choke on you can burn the catalytic muffler up and possibly start a carpet fire in the car. That's happened.

    The sooner you dump this mess the better.

    Maserati Other | eBay
    Image Unavailable, Please Login
     
  3. William Abraham

    William Abraham Formula Junior

    Nov 21, 2010
    830
    London, UK
    Full Name:
    William Abraham
    #3 William Abraham, Feb 5, 2014
    If you go to Enrico's site there is a discussion about the glowing exhaust heat so read the thread there. I cannot add to the experts views above
     
  4. William Abraham

    William Abraham Formula Junior

    Nov 21, 2010
    830
    London, UK
    Full Name:
    William Abraham
    #4 William Abraham, Feb 5, 2014

Share This Page