surge in carb

Discussion in 'Classic Mustang Specific Tech' started by chris in knox, Dec 10, 2003.


  1. chris in knox

    chris in knox New Member

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    Hi everyone, I'm new to the net, but not to the mustang. I 've had my Mach1 for 7 years. It's got an original 69' intake and autolite 4300 4v with a FMX 3-speed tranny. The problem is it surges when your trying to cruise at a steady speed. I had the Distributor rebuilt with an ignighter ignition and the 4300 is branny-new. I've played with the advance to no end. The only constant in all of this is the intake. Could this be the culprit? By the way the motor is the original 351w. I rebuilt it (with help). I had it bored alittle (0.30 over) with a step over stock cam. I'm thinking of selling the intake/4300 setup for an alluminum holley setup. Do you think this will solve the surge? Thanks for your help.
     
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  2. 68GEETEE

    68GEETEE Member

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    Hard to say, but I would lean towards a vacuum leak or manifold leak as the culprit.
     
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  3. 94CobraPace

    94CobraPace Founding Member

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    Sounds like it could be running a little lean. Try to richen out a little and see if the helps.
     
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  4. chris in knox

    chris in knox New Member

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    I heard the trick to finding a vaccum leak is to let the engine idle an spray carb cleaner around the intake area and see if the engine rpm's go up. I tried this and there doesn't seem to be any leaks.
     
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  5. chris in knox

    chris in knox New Member

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    I adjusted the screws to no end. Before I bought the new 4300, the old one was really rich( thats just where it ran the best) The surge has been constant throughout. That's why I'm leaning towards a new intake because that's the only thing I haven't changed( but what do I know?) I was hoping someone else has had this problem so I could copy them (guess I'm blazin my own trail on this one). Thanks for replying to me.
     
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  6. Ozsum67

    Ozsum67 Too much thin air Founding Member

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    If you don't have a vac leak, try unhooking and plugging the vac advance lines. My old distributer did that because the advance sprins under the points plate were weak. It ran fine after I disconnected it while I was waiting on my new dist.
     
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  7. chris in knox

    chris in knox New Member

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    Thanks for the reply. The distributor is new throughout( a guy in Oregon, Distributor Dynamics I think, went all through it) The surge was the same before and after the rebuild. Pony Carburators is convinced it's a timing advance problem. I spent hrs. riding around with alittle wrench, advancing and retarding the timing. The car runs better and better but still surges when you try to cruise at a steady speed. It's like a little man is in the carb. spraying extra fuel.
     
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  8. 68GEETEE

    68GEETEE Member

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    how about your fuel system? How old is the pump and filter?
     
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  9. pabear89

    pabear89 Active Member

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    Hi and Welcome to the site,
    can you discribe the Surging it is doing a little clearer?
    At what speeds or is a constant thing?
    prev replys have covered the main look ats, :nice:
    But when it surges how much increase are you talking about?

    need more input to make the brain function. :D

    PB
     
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  10. Ozsum67

    Ozsum67 Too much thin air Founding Member

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    That doesn't really mean anything. I'm telling you. it sounds like the springs are weak and the timing is advancing too much. Did you disable the vac advance to see if it went away? Pony carb guys are gurus.
     
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  11. chris in knox

    chris in knox New Member

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    Thanks for the reply(nice car)
    The surge is just enough to feel it in your but and only at steady speeds, like if your trying to cruise at 40mph behind a line of traffic or some residential area. If you excellerate it will go away. It might even be something that I should just live with, but it bugs me to no end (I don't hide it well do I?)
     
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  12. chris in knox

    chris in knox New Member

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    No I didn't disable the vac. advance ( it's probably the one thing I didn't do) I can't do anything right no cause it's up on jack stands. It's possible that your right but the distributor has everything new in it, including the springs. It will be one of the first things I do this spring, just for peace of mind. Thanks for the advice.
     
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  13. chris in knox

    chris in knox New Member

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    The pump and filter are new ( discouraging isn't it?)
     
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  14. pabear89

    pabear89 Active Member

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    :D that's my Baby,

    Oz may be right.
    The advance may be working back and forth.
    There may be a vac leak elsewhere.
    If you have p/b or other vac connections it may be drawing the advance to move and release.
    Try unhooking any vac line that is not needed[except trans line if auto]
    and take a short test drive.
    If it is gone then hook 1 line and retest.
    sometimes it is the process of elimnation that will tell the tale.

    PB
     
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  15. chris in knox

    chris in knox New Member

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    I'm printing this all out so I can try it in the spring. Does this mean that I should keep the ford intake and 4300 or would I benefit from a Holley setup?
     
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  16. pabear89

    pabear89 Active Member

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    The benefits from swapping intakes and Carb is losing that extra weight to start.
    And maybe a pony or two.

    PB
     
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  17. pabear89

    pabear89 Active Member

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    When you say everything, Did they replace the breakerplate too?
    Not to many places change them and when the little bushings go bad their a pain
    to make it run correctly.

    PB
     
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  18. chris in knox

    chris in knox New Member

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    To be honest with you I have no idea if everything was changed I just know thar he kept my original distributor and gave me a rebuilt one that was suppose to be better than original. The shafts are all 1969 so I didn't think it was anything to worry about. His claim to fame is that he's some kind of guru for the distributor ( I talked to him on the phone, he seemed to be a nice ol' guy, who cared about distributors and Mustangs) I know it ran like a champ when we put it back in (the igniter really made a differance) I had talked to him about the surge before I sent him the distributor so he could look for the things that your talking about, but whether he actually did is another thing. If I do the things you guys are talking about I should find it.
     
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  19. 10secgoal

    10secgoal Active Member

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    Vac. leak

    This sounds familiar. O.K. first the the screws I think you are talking about are the idle mixture screws and they do nothing except at and just off idle. Have you got a vac guage ? It really comes in handy for many things. Like doing the idle mixture screws. Hook up the gauge at idle. If you see the needle jumping around horribly its more than likely a vac leak. Now disconnect every vac hook up you got. Does it get better ? If it does it's in one of the lines you took off. If not, it's a good time to get out carb cleaner. If the needle just just a bit to start I would then say it's only timing or your idle mixture screws. good luck ?
     
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  20. chris in knox

    chris in knox New Member

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    Thank you for the reply, I'll add it to all of the advice I've gotten so far. I'm going to do all of this in the spring. This website is awsome! Now I got to go buy a snowblower :notnice: Thanks again!
     
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