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***Engine Guys, need help with running problem

Discussion in 'The Hokey Ass Message Board' started by 50mercfan, Oct 22, 2008.

  1. 355 sbc, 700r4, 57 chevy. holley street avenger carb. accel hei distributor. autolite "big" plugs. the engine will start right up and run fine. every few seconds it dose what i can only describe as a "flutter" and vibrates slightly. dose this consistently. also, it falls on it's face at take off, i'm talking about normal take off, not launching from the line. i started looking for vacuum leaks. all i could find is when i spray starting fluid under the secondary pump it will almost kill the enigine. rebuilt the carb and changed the pump diaphram. no change. engine vibrates the car at high way speeds, it has solid motor mounts. any ideas?
     
  2. 53sled
    Joined: Jul 5, 2005
    Posts: 5,817

    53sled
    Member
    from KCMO

    was the rotating assembly balanced?
     

  3. yes, i bought a 70 chevy truck just to get this engine. i drove the truck for a while. it ran fine.
     
  4. SinisterCustom
    Joined: Feb 18, 2004
    Posts: 8,277

    SinisterCustom
    Member

    This sounds like a vacuum leak....
     

  5. Fat Hack
    Joined: Nov 30, 2002
    Posts: 7,709

    Fat Hack
    Member
    from Detroit

    Is the carb new..or used? It sound slike you could have a vacuum leak around the throttle shafts. Common problem on older Holleys.

    Also:

    *Do you have a vacuum advance distributor? If so, is it running off of ported or manifold vacuum, and is the diaphram good? (GM cars normally use manifold vacuum for the advance).

    *Float level too high, bad needle and seat or too much fuel pressure? Fuel dripping into the venturis past the needle and seat can cause symptoms similar to what you're describing.

    *Distributor bushings good? A wobbling distributor shaft can do some funny shit.

    *Also look for a vacuum leak at the plug (or fitting if so equipped) right behind the carb and off to the passenger side. Typically where you might hook up power brakes. Spraying ether near the secondaries side of the carb would put you right by this plug/fitting.

    Hard to diagnose stuff like this over the internet, but that's a few ideas to get ya maybe into the ballpark???
     
  6. colorado51
    Joined: Feb 24, 2003
    Posts: 1,576

    colorado51
    Member

    I'd check the float levels and the fuel pressure first. Pressure should be between 4 - 7 lbs.

    Then maybe set the air/fuel mixture using a vacuum gauge.

    There are a lot of other stuff to check too, but I would start with the basics first.
     
  7. Duration
    Joined: Oct 2, 2006
    Posts: 543

    Duration
    Member
    from Wayne, MI

    sounds like a vacum leak to me. if starting fluid makes it speed up then you missed something in that area.
     
  8. hack, the throttle shafts will wiggle slightly, i thought this was wrong, so, i get another one off my shelf and it's exactly the same. the carb is used but very few miles. the guy i bought the truck from bought it new. it ran fine in the truck, but, it's been sitting for a couple of years. the fuel pump is new stock replacement, nothing high performance. the vacuum port for the power brake booster has a power brake booster connected to it. i put a hose clamp on it to make sure it wasn't sucking air. that is the area where the problem seems to be. i changed base gaskets also. i have the vacuum advance hooked up to ported vacuum not manifold, i'll try that to see if it makes a difference. and i'll check the distributor shaft also.

    i drove it at high way speeds tonight. at cruise speed with the converter locked up you can feel and hear this low speed "flutter". when i give it a fair amount of throttle it straightens up and runs fine.
     

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