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My SK Synchrometer Appears Broken

Discussion in 'Technical Q&A' started by donaldh2o, Mar 20, 2004.

  1. donaldh2o

    donaldh2o Karting

    Nov 10, 2003
    143
    Irvine CA
    Full Name:
    Don
    Trying to synchronize the weber carbs on my '76 308 and the synchrometer is reading very high (10 or more). My understanding is that it should read about 3.5 to 5.

    But I just discovered that the STE SK Synchrometer is reading 7 while its just sitting upright on the bench. No matter where I place it, it still reads 7. If I tilt it upside down then it goes to zero.

    Shouldn't it read zero when sitting upright on the bench?

    How do I calibrate this thing? Or do I have to throw it away and buy another one?

    Mine has the #118 extender.
     
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  3. donaldh2o

    donaldh2o Karting

    Nov 10, 2003
    143
    Irvine CA
    Full Name:
    Don
    OK, I took the synchrometer apart in an attempt to repair it. It's made entirely of plastic except for the axel, axel screws and a small coil spring.

    There was nothing obviously broken so I concluded that the spring just lost its tension. This makes me wonder how long the spring has been getting weak and if my previous carburetor adjustments were erroneous.

    For the cost of nearly $50, this is very cheaply made. A $20 Timex watch is much more sophisticated than this thing. At least it should have a calibrating adjustment. But it has none.

    So now totally sceptical of the accuracy of the STE SK flow meter, what do I use to set the carbs? From what I've found surfing the internet, there are three choices: two with springs in them - the STE SK and an analog dial-type in the JC Whitney catalog; and one that uses a bouncing ball - known as the UNISYN.

    My gut feel is the Unisyn would be the most accurate.

    More on this later.
     
  4. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
    TN
    IME the Unisyn isn't very accurate. The floating red ball just doesn't seem to work that good. Just my opinion.
     
  5. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
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    Philip
    Don
    Sorry, I thought I had replied on this earlier but don't see my post.

    They read "0" at rest or when you shake the unit around.

    I've found the level (5, 6, 7, 9) is less important than the relativity between the throats - remember you are trying to sync the airflow across the carbs.

    You can always do what I've done and install air nipples that you can connect manometer tubes too. Gives a much more precise reading. Alternatively, a new SK unit is only $40. I think the SKs are more precise than the ball in the tube units.
    Philip
     
  6. bill308

    bill308 Formula 3
    Silver Subscribed

    May 13, 2001
    1,082
    Windsor, CT
    Full Name:
    Bill Sebestyen
    I'm with Philip on this one. In my opinion, the BK and SK Synchrometers are far superior to the Unisync. Having said this, I was unhappy with my BK's as one still had to move the instrument from barrel to barrel and remember what the readings were for comparison purposes.

    I finally bit the bullet and installed vacuum fittings (stainless steel barbs) in the bosses of the intake manifold which formerly held the tubing manifold that evacuates the charcoal canister. For synchronizing my webers, I now attach vaccum hoses to the barbs at one end to a bank of mercury manometers at the other end and measure manifold vaccum simultaneously on all 8-cylinders. The manometers I use are normally used by motor cycle guys. This setup is very sensitive and provides repeatable readings. The effects of adjusting the air flow on one cylinder are seen immediately as is its effects on all other cylinders. Synchronization is perfect when all mercury columns are at the same height. This setup works particularly well for off idle measurements where one actuates the throttle and observes the movement of the mercury columns. Also, your hands are free to make any additional adjustments.

    When synchronization is complete, I soft plumb the charcoal canister evacuation circuit to the open barbs.

    If anyone is interrested in some photos of this setup, email me as the photos have captions that would be difficult to read on this board.
     
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  8. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
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    Philip
    Bill
    We've done the same plumbing. I run mine to a MAP rather than the charcoal, but some idea. And yes, visibility and accuracy are much improved.

    I'm curious, how much vacuum (inches of mercury) do you see at idle?
    Philip
     
  9. bill308

    bill308 Formula 3
    Silver Subscribed

    May 13, 2001
    1,082
    Windsor, CT
    Full Name:
    Bill Sebestyen
    Philip,

    All cylinders are 25-26 inches of Hg.

    Is the vacuum signal going to map part of an Electromotive system?
     
  10. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
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    Philip
    Yes Bill, that's right.
    I see a lot less vac at idle with the big cams. I do get that kind of vac at higher rpm (1200).
    Philip
     
  11. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
    2,279
    Roseburg, OR
    Full Name:
    Hans E. Hansen
    Do the mercury columns 'pulse' up and down? I thought that was the biggest problem with the 'ball in a column' type of syncrometer.
     
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  13. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
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    Philip
    Hans
    The mercury is pretty stable unless the motor audibly stumbles.
    The SK is pretty consistent too -- doesn't "vibrate" like the ball in the tube types.
    Philip
     

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