Oil build up on 2nd cylinder and misfire

Discussion in 'Ranchero Tech Help' started by polarfuchs, Sep 6, 2021.

  1. polarfuchs

    polarfuchs In First Gear

    Messages:
    15
    Location:
    Tucson
    Hi!
    I just bought my '73 500 (351c) last weekend.
    The engine was running quite rough so I decided to do a basic tuneup:

    • new plugs (.40 gap)
    • new plug wires
    • new cap + rotor
    • new coil (MSD)
    • new fuel filters (at the carb and a few feet in front of it was already a generic fuel filter installed so I replaced it)
    As I removed the plugs the plug of the 2nd cylinder was completely soaked with oil and just black.
    I did a compression test and all cylinders had been in the same range between 110 & 130 psi.

    I started the engine and it was running much better but I still got that misfire when I did slowly increase the RPM. Unfortunately, I do not have a tach installed so I cannot really get the RPM reading when the misfire is happening.

    Maybe "misfire" is the wrong word here as I hear the banging in the carb?

    Anyways...

    I checked the new plugs again and the plug of the 2nd cylinder is quite black while the others are looking ok to me.

    On the driver's side, the bottom of the carb seems to leak. I can smell gas. Here's a closeup of the carb's bottom:

    [​IMG]

    Could that cause the misfire?
    Could that cause the black plug on the 2nd cylinder?
    Will I have to rebuild the carb?

    If I have to rebuild the carb (2 barrel carb) would it make sense to just buy a new one and go for a 4 barrel in case I can make this fit?

    Thanks in advance!
     
    Ran Man likes this.
  2. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
    14,003
    Location:
    New Braunfels, TX
    All carb gaskets will eventually leak. Fel-Pro does make the two gaskets you need, but I think you may have two separate problems: the gasket leak, and oil intrusion into cylinder 2. My '74 Squire I had years ago did have some oil seepage, but as long as I kept the oil changed and cleaned the plugs regularly, it was not a problem.
     
  3. 5.0 Chero

    5.0 Chero Bahumbug Staff Member

    Messages:
    14,289
    Location:
    Prunetucky California
    Are you sure it was oil and not fuel? Also did you change the points? Did you check/ set the timing to much advance can cause the "Banging" in the Carb as can the firing order being off.
     
    The Wrench likes this.
  4. polarfuchs

    polarfuchs In First Gear

    Messages:
    15
    Location:
    Tucson
    Thanks. I just ordered the gaskets.
     
  5. polarfuchs

    polarfuchs In First Gear

    Messages:
    15
    Location:
    Tucson
    Thanks. I just ordered the points. After installing and setting them (should be 0.017" if I have the right specs) I will check the timing.
    The banging in the carb only happens when I do a moderate acceleration. I will double-check the firing order. I did change the routing of the wires for cylinders 7 & 8 and do not run them in parallel to each other - I read this might also cause issues, but I did not yet start the engine since then.
     
  6. polarfuchs

    polarfuchs In First Gear

    Messages:
    15
    Location:
    Tucson
    Here are two photos of the old plugs.

    Starting with cylinder 1 from the right.

    [​IMG]

    Plug of 2nd cylinder:

    [​IMG]
     
  7. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
    14,003
    Location:
    New Braunfels, TX
    Do you have a dwell meter? The initial gap is only to get you to be able to start the car. Then you put on your dwell meter, set it to maximum dwell (30° IIRC), then set your timing. The reason for doing it this way is to give you the maximum amount of miles on your dwell setting, as a change in dwell causes a change in timing. And that timing change retards the timing, robbing you of performance.
     
  8. polarfuchs

    polarfuchs In First Gear

    Messages:
    15
    Location:
    Tucson
    Thanks for that info! I just went to Harbourfreight to get a dwell meter.
    But I guess I found the culprit!

    The pushrod of the intake valve of cylinder 7 was bent and laying in the cylinder head. I did install a new one and turned the engine several times by hand. The valve was opening and closing. So I did start the engine et voila! Nice and smooth idling, acceleration is also fine, no more misfire or backfire!

    I will still follow all your tips!

    Thank you so much for your help!!!
     
  9. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
    14,003
    Location:
    New Braunfels, TX
    Hey, that's what we're here for--to show off to each other! Just kidding, we're here to help each other restore our rigs and keep them on the road.
     

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