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Thread: Motor not running smoothly

  1. #1
    Speedster Member
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    Motor not running smoothly

    Made it out to SB Sunday, stayed a couple days, saw lots of Studes, bought some parts at the swap meet, went all through that really neat museum, made it back home (had a prior committment), the Hawk ran flawlessly for the most part, with the following exception.

    It seemed that it was constantly "surging", as if it was momentarily losing power and then getting it right back in a matter of seconds.

    Since getting back, I checked the fuel flow in the carb and it is nice and smooth (no spitting), checked the condition of the plugs (perfect), checked for air/vacuum leaks (found none), points and plug wires all ok, distributor contacts clean.

    I'm at a loss as to what to check next. At idle, you can hear the rpms begin to pick up speed for a while (about 50 rpm or so), then drop back down.

    Occasionally, the motor seems to 'miss a beat', like one spark plug simply chose not to fire, just one time, but only once in a while.

    While driving at steady highway speeds, this surging I speak of "feels" like a plug loads up momentarily and then cleans itself off and it does it constantly, on and off, on and off, but no plugs show any signs of oil fouling.

    At idle, it "seems" like it has a vacuum leak that just comes and goes.

    Please, someone help me out here and give me a clue what I should be looking for.


    1962 GT Hawk 4sp

    1962 GT Hawk 4sp

  2. #2
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    Sometimes surging is caused by an overly lean mixture, but if that's the case, the plugs would probably have a white color to them as opposed to a more normal tan. If too lean, sometimes the surging stops for just a bit when you give it some gas because the accellerator pump squirts extra fuel into the mix.

    However, since it also varies in speed at an idle, I'd tend to think it's more something mechanical as in something being loose or worn. You might make sure the choke and throttle plates aren't loose or the throttle shaft bushings worn, loose and sucking air. You might also check to see how much play is in the joint between the throttle and gas pedal. I doubt they're worn bad enough to have too much slop, but it wouldn't hurt to look.

  3. #3
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    I've thought about your car some more and I think I'd remove the air cleaner, unhook the return spring on the carb and see if there's play in the throttle shaft that goes through the carb. When the bushings become badly worn, they'll suck air and lean out the mixture. Some carbs have replaceable brass bushings while others have nothing replaceable, just a worn carb body. If that's the case they can sometimes be drilled out and bushings inserted. I have a badly worn hole on the pot metal carb of a Kohler engine that caused surging and was very pronounced at an idle. As commonly found, it's on the side the spring and throttle linkage attach to. Rather than spend time and money fixing it right, I simply removed the throttle shaft from the carb, slipped an O ring over it and stuck it back together. The O ring seals the leak and it's worked fine for years now.

  4. #4
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    I have to agree with John--a worn throttle shaft is a likely cause of your problems. I would check the shaft and the carb body. If it is the shaft only, its an easy fix--just replace it. If it is the body too, almost all of the older carbs can be reamed and bushed. I would take it to a good carb shop and see what they can do. The fix may cost a few dollars, but remember that that little hole is sucking dirt into your engine too.

    jj

  5. #5
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    To both John and J.Jones, I just had the carb professionally rebuilt by a known and respected forum vendor. I wouldn't think that he'd let a worn throttle shaft slip by....at least not for the money I paid out for the rebuild.

    Tell me though, besides looking for 'freeplay' in the shaft, would simply spraying WD40 or something similar around the throttle shaft where it enters the carb body while the motor is idling, be a reliable method for determining if indeed there is an air leak at that point?

    Also, regarding the spark plugs, the center electrode and the ring of the plug body itself, indicated a balanced A/F mixture.....however the top of the arm (which is the part that is "bent" to get the correct gap setting), is powdery grayish-white.

    I adjusted the A/F screws as is recommended....that is, back them out evenly so that the motor will at least run, then gradually turn each screw back in (clockwise) in gradual increments until the idle drops about 50 rpm.....then turn them back counter clockwise 1/2 turn.

    If indeed, the mixture is running lean, how do I correct that?.....simply by turning the A/F screws ccw some more?

    Karl

  6. #6
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    Make sure the distributor clamp is tight. That drove us nuts on a trip once.

    Frank Starr

  7. #7
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    Concerning the grayish white on the plug, the mixture certainly isn't overly rich and may be just a tad lean, but personally that's what I'd be shooting for. And on the bright side, you must have excellent oil control on your engine.

    WD 40 or even dripping a little heavy oil around the shaft should make a difference if there is indeed excessive play in the shaft.

    I'm not saying this is the problem, but I once had a tractor start running very rich, sometimes flooding out, then began running very lean at times but normally other times. Ends up the culprit was a small chunck of rubber from the fuel line that had to have come from the inline filter area. I'm guessing that it stuck in the float valve for a bit, causing the rich running and flooding and finally got into the float bowl where it would sometimes partially clog the main jet.

    It's funny how when having problems, you look for commonalities and my tractor had none whatsoever UNTIL I found the chunk. Then it all made sense. As long as I find the problem, I find troubleshooting rewarding. However, it can be quite frustrating at times!

    By the way, since it seems the fuel air mixture is optimal to slightly lean, what shape are the plugs in and what gap do you have them set at? If the mixture is a little lean, it's going to take a better spark to ignite it adequately. Wider gaps are preferable on lean mixtures IF you have enough electrical get up and go. If your ignition energy is merely adequate, a wide gap and lean mix are going to magnify the lean surging. If you can't find anything in the fuel-air department that seems to be the cause, here's something you could try. If the idle rpm changes rather consistantly, you could disconnect one plug wire at a time and see if the surging is confined to one particular cylinder. If it doesn't make any difference and it's electrical, then it has to be something common to all cylinders such as coil, points etc. Speaking of which, does there seem to be any oil leaking out of the coil? Whenever I found one doing that, it was because I was looking for a cause of hard starting and or irregular missing. If everything electrical checks out, you could always unplug the four plug wires from the cylinders that are fed off of one side of the carb. You'll have to speed the idle up some, but since it will be firing on every other cylinder, it will run. If the problem is in one side of the carb, you should be able to tell a difference. Once had a Carter carb on a truck that would idle on four but run on eight. Never did find the actual problem in the carb, even after having it apart several times, new kit and so on, but I suspect a fracture or other wierd problem in the idle circuit on one side.

  8. #8
    President Member Laemmle's Avatar
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    I had the exact symptoms on my Avanti........turned out the fuel filter had to be changed.........don't laugh, it's true!

    quote:Originally posted by MagikDraggin

    Made it out to SB Sunday, stayed a couple days, saw lots of Studes, bought some parts at the swap meet, went all through that really neat museum, made it back home (had a prior committment), the Hawk ran flawlessly for the most part, with the following exception.

    It seemed that it was constantly "surging", as if it was momentarily losing power and then getting it right back in a matter of seconds.

    Since getting back, I checked the fuel flow in the carb and it is nice and smooth (no spitting), checked the condition of the plugs (perfect), checked for air/vacuum leaks (found none), points and plug wires all ok, distributor contacts clean.

    I'm at a loss as to what to check next. At idle, you can hear the rpms begin to pick up speed for a while (about 50 rpm or so), then drop back down.

    Occasionally, the motor seems to 'miss a beat', like one spark plug simply chose not to fire, just one time, but only once in a while.

    While driving at steady highway speeds, this surging I speak of "feels" like a plug loads up momentarily and then cleans itself off and it does it constantly, on and off, on and off, but no plugs show any signs of oil fouling.

    At idle, it "seems" like it has a vacuum leak that just comes and goes.

    Please, someone help me out here and give me a clue what I should be looking for.


    1962 GT Hawk 4sp

  9. #9
    Silver Hawk Member
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    Greetings, All,

    One thing we old guys have to remember is most of what we learned about reading the color of a spark plug insulator is not necessarily valid with today's fuel and oil. The removal of tetraethyl lead and the addition of methanol, ethanol, MBTE, and who knows what else, plus synthetic oils. has rendered the black art of tailpipe and plug insulation color unreliable at best. Today, as I was pouring gas into the lawn mower, I noticed this batch was sort of greenish in the sunlight. Now, how is that gonna look on a plug?

    thnx, jv.

    PackardV8

  10. #10
    President Member studelover's Avatar
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    Did you check your carb base gasket? brake fluid if it revs thats it. causes car idle to run up and down.

    Studebakers forever!

  11. #11
    President Member ROADRACELARK's Avatar
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    While you're at the distributor, check the vacuum advance unit. Use either a hand vacuum pump (Mighty-Vac), or a long piece of vacuum hose you can suck on to check for a leak. If it's leaking, you won't have any ignition advance, (slugish throttle response) and you WILL have a vacuum leak. Hope this helps. Fantastic meet in South Bend.

    Dan Miller
    Atlanta, GA

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    Road Racers turn left AND right.

  12. #12
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    Karl, you could also be having sparkplug wire issues, like one could be shorting to ground or crossfire into each other if the age of the wires is unknown.

  13. #13
    Silver Hawk Member 53k's Avatar
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    Have you put a dwell meter on it and run the engine at varying speeds? Could be worn distributor shaft bushings or sticky weights.


    [img=right]http://www.frontiernet.net/~thejohnsons/Forum%20signature%20pix/R-4.JPG[/img=right][img=right]http://www.frontiernet.net/~thejohnsons/Forum%20signature%20pix/64L.JPG[/img=right][img=right]http://www.frontiernet.net/~thejohnsons/Forum%20signature%20pix/64P.jpg[/img=right][img=right]http://www.frontiernet.net/~thejohnsons/Forum%20signature%20pix/53K.jpg[/img=right]Paul Johnson
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  14. #14
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    Remember this little problem I was having?

    Well, I finally tracked it down and found that it was a combination of two things. First there was a small amount of leakage in the (supposedly new) spark plug wires. This I determined by observing the motor running in the pitch darkness of the garage at night. Every now and then besides the usual "corona effect", there was this slight arc occuring from one wire to another.

    Replacing the wires "solved" that part of the problem.

    The highway surging was found to be caused by two of the intake manifold bolts being loose....one almost to the extent of being literally finger loose. Applying a little muscle to those and checking the rest and viola....NOW the 289 purrs the way it was intended on the highway as well as having a relatively smooth idle.

    So now, it's on to figuring how to quieten down that clacking fuel pump. Looks like my only recourse is to replace it and hope that takes care of it. It's embarrassing to pull into some 'cruise-in' spot and having the thing clack, clack, clack away like a washing machine with a couple teeth broken off one of its gears.

    Thanks to all that offered ideas and helpful hints as to what to look for in resolving those problems. You guys are the greatest!

    Karl


    1962 GT Hawk 4sp

  15. #15
    Silver Hawk Member
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    Hi, MagikDraggin'

    Good to hear your problems were small and easy/inexpensive to fix.

    Is your fuel pump a genuine-made-for-Studebaker pump or a Mopar pump someone has modified with a bigger hammer? We see many Mopar pumps which have been bent too much and make the noise you describe.

    thnx, jack vines

    PackardV8

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