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Hesitation above 3000 rpm

Discussion in 'The Garage' started by akbound, May 25, 2004.

  1. akbound

    akbound 1/2 ton status

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    when I get to 3000 rpm my Blazer hesitates and doesn't really seem like it wants to rev higher. It will, but it just doesn't climb like it should. I just bought this about 3 weeks ago and the seller said the carb (4MV) was just rebuilt. It was wicked rich (blew black sh*t all over the cars parked on each side of me), but I leaned it out. Any ideas?

    TNX,
    Don: 76 Blazer 350/465/205
     
  2. fatboy

    fatboy 1/2 ton status

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    what carb is it? sounds like you have a lean spot. Wide open throttle or gradual speed? You may just add a stiffer spring under the primary metering rod if its gradual speed or the WOT you may need to change rob and jet configuration. We need more info on carb and who did the work.
    Hope that helps some /forums/images/graemlins/burb.gif
     
  3. SHAWNSTER

    SHAWNSTER 1/2 ton status

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    i had the same thing wrong with my blaze when i bought it, we took it out for a test run and i had great throttle response from a stop, but above 2500 rpm the motor would start to bogg down, the carb was shot-even though it had just been rebuilt?
     
  4. bigyellowjimmy

    bigyellowjimmy 1/2 ton status

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    Start with the simple stuff...air filter, fuel filter, cap, rotor, plug wires and plugs. Check the timing. /forums/images/graemlins/thumb.gif
     
  5. akbound

    akbound 1/2 ton status

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    Thanks to all!!

    It is the original Quadrajet 4MV. Since I have bought it I have changed the following: air, fuel, & oil filters, oil, fuel pump, heater core, belts, hoses, coolant, added headers & dual el cheapo turbos 2.25 exhaust exiting behind the doors, and Accel shorty spark plugs.

    I also own a 78 LeSabre with a 403 and a Quadrajet. I can really tell when the secondaries come in on it. With the Blazer I am not really sure if and when they do.
     
  6. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    It's been my experience with the Quadrajet, that you know when those secondaries open.

    Check to see if the linkage is bound up maybe, because it sounds like the secondaries aren't opening.
     
  7. bigyellowjimmy

    bigyellowjimmy 1/2 ton status

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    Sounds like you are whipping it into shape! You didnt mention the cap and rotor.......you might want to look to see if they are worn, very common for a worn rotor to cause a miss at higher RPM. That way you wont get frustrated tuning the carb if the cap and rotor are aggrevating or causing the problem. /forums/images/graemlins/thumb.gif
     
  8. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    Timing.
    Cap and rotor. Spark plugs. Spark plug wires. An oscilliscope will help you track down which cylinder is missing or doing something funny.
    Fuel filter? Fuel pump might be okay but Fuel psi?
     
  9. akbound

    akbound 1/2 ton status

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    Looks like I will be getting new wires, cap and rotor today.

    If that doesn't cure it, I will buy a reman carb for $160. The carb that is on it is original, has >200K miles on it, and has been kitted by the PO a couple of times.

    Thanks for all the input.
     
  10. bigyellowjimmy

    bigyellowjimmy 1/2 ton status

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    Good luck, let us know how you make out /forums/images/graemlins/thumb.gif
     

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