New Owner Red 1970 Deville Convertible - Page 6
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The Classic Cadillac Forum Discussion, New Owner Red 1970 Deville Convertible in Past Cadillac Vehicle Discussion; I think the idling problem is fixed and it runs a bit smoother now. I replaced the vacuum advance canister ...
  1. #76
    klinebau is offline Cadillac Owners Member
    Automobile(s): 1970 Deville Convertible Red
    Join Date
    Jul 2012
    Posts
    75

    Re: New Owner Red 1970 Deville Convertible

    I think the idling problem is fixed and it runs a bit smoother now. I replaced the vacuum advance canister and cleaned up the weights in the distributor, but I think the problem was a vacuum leak. The temperature sensor on the air cleaner was leaking. I didn't notice when setting the timing because I would typically pull this line and plug it. I will probably just leave that line plugged and not run heated air bypass valve.
    70eldo likes this.

  2. #77
    klinebau is offline Cadillac Owners Member
    Automobile(s): 1970 Deville Convertible Red
    Join Date
    Jul 2012
    Posts
    75

    Re: New Owner Red 1970 Deville Convertible

    Still not happy with the idle. It will idle at the right speed in drive (600), but is rough. When in park, it still has a rough idle but the exhaust will also randomly chuff every second or so (chuff... chuff, chuff, chuff.... chuff...). I've been working on it on and off for a couple of months now. The car runs fine everywhere else except at idle.

    So far I have
    - Adjusted the idle mixture about a dozen times with various combinations of lean/rich settings. The idle mixture screws do affect RPM and it will idle low so I don't think I have a major vacuum leak. No setting will give a smooth idle.
    - Confirmed no vacuum leaks. I previously replaced all vacuum lines but I have also disconnected and plugged all the vacuum lines to test that the problem remains. Using carb cleaner, I have sprayed around the engine bay (intake manifold, carb base, vacuum lines, brake booster, etc.) with no changes to idle quality.
    - Replaced distributor and most ignition components (points, condenser, rotor, cap). Previously, I noticed that the timing was off over 4 degrees at idle between cylinder 1 and 4 and is the main reason I replaced the dizzy.
    - I replaced the plugs and wires when I first purchased the car and they only have about 350 miles on them.
    - I replaced the carb with a rebuilt unit shortly after purchasing.

    Today I made some interesting observations. Using the dial back function on my timing light (90*), I looked at timing for cylinders 3, 8. The timing marks were jumping around wildly (10 degrees). The timing on #1 and #4 is rock steady at 8 BTDC. I pulled the #8 plug and it looked oil fouled (#3 looked fine). It didn't seem really bad compared to other pictures I saw online, but the insulator was black along with the electrode and ground. I cleaned up the plug and put it back in, but it didn't fix the idle.

    What should I do now? I should perform a compression test. I don't have one currently, but will get one. Would new plugs fix the problem? I haven't replaced the plugs since I bought the car and they could have fouled due to previous mis-adjustments (bad carb, vacuum leaks, etc.) I am guessing that the valve seals have deteriorated or are missing. What are the chances that this problem could be fixed with with new valve seals? What else should I consider?

  3. #78
    klinebau is offline Cadillac Owners Member
    Automobile(s): 1970 Deville Convertible Red
    Join Date
    Jul 2012
    Posts
    75

    Re: New Owner Red 1970 Deville Convertible

    Been thinking about this overnight. The #7 plug was also a bit fouled, but not as bad. That means both rear plugs are fouled. It seems most likely to be a valve guide seal problem. I am still going to check compression, but am likely going to replace valve guide seals. I think I can replace them without removing the heads.

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