1968 Riviera 430 low vacuum reading on gauge

Discussion in 'The Bench' started by 1969briviera, Apr 25, 2015.

  1. 1969briviera

    1969briviera Antique Gold Poly

    We only get 15" of vacuum steady reading on vacuum gauge at idle (red area gauge late ignition timing).
    Ignition/carb are original to the car.
    Any suggestions on what we could check for vacuum loss somewhere?

    Thanks.
     
  2. Rivman

    Rivman Senior Ottawa Buick Guy

    On a '68-'69 Riviera Rob, it could be any one of the many components in the vacuum headlight setup, a simple split hose end, or a cracked manifold vacuum distribution valve on the lower firewall. The heater/AC control system also uses vacuum to control vents and the temperature door. :Do No:
     
  3. 1969briviera

    1969briviera Antique Gold Poly

    Thanks Randy. Yes i know what you mean. We have to check the less easy to get to areas.
    But maybe it could be more related to engine (mechanical)....
     
  4. CJay

    CJay Supercar owner Staff Member

    Or you could just have late timing:Do No: What is your initial advance set to?
     
  5. 1969briviera

    1969briviera Antique Gold Poly

    Distributor is original to the car and timing is set to original specs...thanks.

    We had to adjust the rpm idle screw because it did not make any contact with the throttle arm. Throttle response is good. Idle is steady (550 rpm in D range).

    We will check air/fuel mixture, the two screws in front of the carb (although it runs smooth at idle).
     
    Last edited: Apr 26, 2015
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member


    The fast idle screw doesn't contact the throttle arm, it contacts the fast idle cam, but only when the choke is closed.


    Vacuum leaks are usually broken vacuum lines, or a bad carburetor to intake manifold gasket.

    Your vacuum advance should be connected to manifold vacuum so that it adds timing at idle.
     
  7. 1969briviera

    1969briviera Antique Gold Poly

    I meant rpm idle screw instead of fast idle screw. I just corrected that.

    Vacuum advance on this car is connected the original way. Just as my own car where vacuum readings show just fine.
     
  8. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Have you checked that the vacuum advance is actually working? What is the ignition timing while the engine is idling?
     
  9. CJay

    CJay Supercar owner Staff Member

    The factory timing is zero degrees on a 430. Wouldn't that account for the less than optimal vacuum? As a test, bring the timing up to 10 degrees and take a vacuum reading. I bet you'll be up around 19"-20"
     
  10. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Jason,
    Is your vacuum advance on your 69 hooked to manifold vacuum. That would boost the idle timing up to 14-18*. I'm thinking his vacuum canister might be bad which would lower his timing and be a vacuum leak also.

    See you at the Spring meet today?
     
  11. CJay

    CJay Supercar owner Staff Member

    Leaving in about an hour. Should be there around 11:30.

    The vacuum advance on my Riv is hooked to ported vacuum. I think I still have it hooked to the ported vacuum switch. I threw away the factory timing specs on that car years ago. Its been "power timed" :TU: The 68 is set to 0* and the vacuum is only 14"
     
  12. 1969briviera

    1969briviera Antique Gold Poly

    The vacuum canister is brand new (AC Delco).
    Ignition timing is stock, we have the initial at 1 BTDC (almost at 0 TDC), distributor is original with original springs.

    It should get 18" to 19" of vacuum via the thermo vacuum switch and ported vacuum port at the carb. My riv is showing 18"-19" of vacuum that way.
    We have to look for vacuum from the headlights, the headlights fall down when the engine is turned off...so there is a leak somewhere we can't find just yet...
     
  13. CJay

    CJay Supercar owner Staff Member

    The headlight actuators more than likely are bad. The actuators bleed off the vacuum and the car winks at you come morning. I resolved that by installing new ones. If you suspect a leak, pinch off, or plug the hose off the intake to the headlights. See if there is an improvement

    As far as Im concerned, your chasing an imaginary problem with the low vacuum reading
     
  14. 1969briviera

    1969briviera Antique Gold Poly

    Well, vacuum is too low that is for sure.
    We will look for the connection you mention and pinch it off, we will see if that helps.
    With the actuators you mean the small ones near the front fender? Not the big vacuum cans near the grille? The big cans seem to operate fine.
     
  15. CJay

    CJay Supercar owner Staff Member

    The car has late timing, so the vacuum will normally be low. Nothing you can do about that. if you want 19" of vacuum, advance the initial timing to 10 degrees.

    As far as the actuators- yes, They get parasitic leaks. They will operate fine. As soon as you shut the car off, they will start to bleed off vacuum until the weight of the lights overcomes the amount of vacuum left in the system. its a common issue. My system did the same thing.
     
  16. 1969briviera

    1969briviera Antique Gold Poly

    I prefer finding the vacuum leak...then check the ignition timing again.
     
  17. CJay

    CJay Supercar owner Staff Member

    Again, the vacuum is supposed to be where it is. I don't think you cant have 0 degrees initial AND 19" of vacuum at the same time.
     
  18. 1969briviera

    1969briviera Antique Gold Poly

    Actually i do have 19 at my own car so it can be better then 15"....
     
  19. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    If that was my car, I would switch the vacuum advance to manifold vacuum. That would give you extra advance at idle. It is easy to do. Try it, you can always switch it back. I bet the engine will like it. There will be no difference at part throttle between ported and manifold vacuum to the canister. At 0* timing, it must heat up when stuck in stop and go traffic. That is relatively retarded timing, and that will heat an engine up fast on a hot day.
     
  20. 1969briviera

    1969briviera Antique Gold Poly

    You mean without the thermo vacuum switch and block off ported vacuum with a hose...then the vacuum canister directly to manifold vacuum on the carb...
     

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