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Spark Modifier ...How Test

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  • Ignition: Spark Modifier ...How Test

    The 61 Hawk is running hot (although it is 95 out in NJ). I was reading the Shop Manual and it says the Spark Modifier could be stuck. I took off the dist. cap and the arm moves do you know if there is a problem? The car runs fine, accelerates good. it's not "overheating" like boiling over or hard start, just getting up around 215 degrees. Probably normal...but the Ethanol Gas is vapor Locking around 220.

  • #2
    Hook up a vacuum source like a MightyVac to the vacuum advance (spark modifier), and pull about 15" vacuum -- you should see the arm move the distributor (point) plate. If the vacuum advance doesn't move, the vacuum advance diaphragm is bad. Also, make sure it holds vacuum -- if it leaks down, that is a vacuum leak and will probably only get worse.

    The movement of the distributor (point) plate by the vacuum advance should be smooth; if it isn't, the plate probably needs cleaning/lubricating.

    Using the MightyVac with the engine running and a dial back timing light, you can check the actual advance that the vacuum advance is giving you, and compare it against what the shop manual says you should get.
    Winston-Salem, NC
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    • #3
      At 95 degrees, if the Hawk has a 2-row radiator, it's gonna run borderline on too hot, unless moving at 30+ MPH. If a 3-row, in good condition, it should be OK, but avoid prolonged idling. Modern 3-rows are available that are equivalent to 5-rows in days of old, if Stude had used such a thing. I have them in all 3 of our Hawks, and temps are very stable, year round.

      As for the spark modifier (a.k.a. vacuum advance) you can check it as r1lark explained, if you have a MightyVac but, if not, you can also use your mouth as a 'MightyVac'. If the motor is not running, just attach a rubber vacuum hose long enough to reach your mouth, and check for it to hold vacuum by sucking the hose as if it were a small straw with ice stuck in it. With the motor running (best), if it won't hold vacuum, and motor idle does not increase, the VA is bad. If it's good, there'll be vacuum you can draw with your mouth, then hold with tip of your tongue, and idle will pick up 200-300 RPM. It's really simple, and I my be making it sound more complicated than it is.
      Last edited by JoeHall; 07-09-2021, 03:11 PM.


      • #4
        So Joe you're saying disconnect it from the carb and suck on that? The tube runs from the carb to the advance.....and I should I feel the tube sucking back on my tongue? Gee I wonder if the wife will get jealous?


        • #5
          OK I disconnected the tube from the carburetor with engine off and I could breath through it...NO VACUUM at all. The carb is producing vacuum. I put a timing light on # 1 cylinder and when the RPM is increased the needle points to IN OP. I assume I did these tests OK? I will buy a new vacuum advance I hope from Stude International or Dave Thiebult if they have one. Can this be changed without removing the distributor....I can see the one little screw inside and the two that it? I'm nervous about doing this as I don't want to remove the distributor, I had an extremely hard time last time getting it in. So would this explain running hot...I hope this solves the problem. I did a six blade fan , 160 Thermostat and new radiator.... I'm getting frustrated.


          • #6
            To check timing, a 'dial back' timing light comes in real handy, dunno how I ever lived without one. Mine includes a tach, to monitor engine RPM simultaneously. A Shop Manual is also handy, since it has pictures, specs, and procedures. It is also helpful to clean the timing marks on the damper, and mark the timing mark (as shown in the Shop Manual) with something like white touch-up paint. At around 700-750 RPM, with Vacuum Advance disconnected, the pointer should be on the timing mark, which is 4 degrees advanced. With a dial back light, you can check it easily, by dialing timing back the light 4 degrees, which will put the light on the TDC mark. The dial backs are simple to operate, and come with simple operating instructions. Just play with it till you get the hang of it, you are not gonna hurt anything.

            Once you have timing mark set at idle, then increase RPM to around 2000 (with the VA still disconnected), and the timing mark should advance maybe another 15 degrees (I forget specifically). The 15 degree advance is coming from the mechanical advance mechanism in the distributor, and it should require 19 degrees dialed back to return the light to the TDC mark.

            Then, reconnect the VA and pick up RPM to around 2000 again, and timing should advance around 40 degrees total. The 40 degrees comes from: the 4 degrees of advance; the mechanical advance, and the vacuum advance. Check it by dialing back the timing light again, till it's on TDC. Note: the VA only kicks in when RPM comes up, because no carb vacuum at idle; only when the butterflies begin to open.

            Again, I am making it sound more complicated than it is.

            Hope this helps.


            • #7
              OK Thanks....I ordered a Vacuum Advance (Spark Modifier) and when I get it in I'll buy a dial back light and follow your numbers.... Do you think this can be changed without removing the distributor....I can see the one little screw inside and the two that it? I'm nervous about doing this as I don't want to remove the distributor, I had an extremely hard time last time getting it in.


              • #8
                Thanks Joe Hall and r1Lark for the advice. I tested and found my advance was no good, got a new one from Dave Thiebuielt (sorry Dave spelling) and installed. Set timing it did help but car was still hot if left idle.....I read the attached old thread (Joe Hall again) https://forum.studebakerdriversclub....ll-overheating and installed a 16 inch pusher fan. FINALLY I can drive with a level of confidence that I won't vapor lock at a few traffic lights! Thanks.