Low rpm stumble

Discussion in 'Troubleshooting & Diagnosis' started by Justin79maro, Dec 22, 2017.

  1. Justin79maro

    Justin79maro Veteran Member

    103
    1
    Jan 15, 2015
    Bonne terre, missouri
    so my car ran great, perfect actually. Then suddenly it got a weird miss or overload like it was running out of gas or running rich, it only happens between 1500-2000 rpm, wot it's a tire burner. Sometimes after I get on it it will do it till I shut the car off and start it the next day it will be fine until I floor it. Sometimes it does it while I'm driving normal and haven't even got on the gas hard. But once it hits 1500-2000rpm it stutters bad and vibrates the exhaust. I changed my plugs and went to 8.5mm wires and a new msd ign coil and it went away for a bit then sudden started again same thing happened. I've changed the foot levels and it still does it. Pulled the plugs and they look perfect. Can't figure it out so I thought I would ask you guys on here. Thanks for the help
     
  2. Gary S

    Gary S Administrator Lifetime Gold Member

    21,082
    308
    Apr 14, 1999
    Bismarck, North Dakota
    What kind of carb? Problems like that can be sometimes caused by the secondaries of a 4 barrel carb opening too soon before the engine is ready for the extra fuel.
     
  3. Justin79maro

    Justin79maro Veteran Member

    103
    1
    Jan 15, 2015
    Bonne terre, missouri
    780cfm quickfuel hr vacuum secondaries
     
  4. Gary S

    Gary S Administrator Lifetime Gold Member

    21,082
    308
    Apr 14, 1999
    Bismarck, North Dakota
    I don't know how the quickfuel carbs work, but make sure that the vacuum secondaries are adjusted right. The vacuum secondaries on a quadrajet can be easily set to open too soon. Maybe your carb is set that way.
     
  5. Justin79maro

    Justin79maro Veteran Member

    103
    1
    Jan 15, 2015
    Bonne terre, missouri
    It's just like a Holley double pumper basically except with vacuum sec. I cleaned the discharge nozzle and it seems like more fuel is comin out. I would test drive it but it's starting to rain so I'll test it tmr.
     
  6. 80sz

    80sz Veteran Member

    2,654
    255
    Feb 2, 2014
    Buffalo,n.y.
    You can adjust the secondary's with a quickfuel. Turn in a quarter turn and slow them down. They could be opening to fast like Gary said .
     
  7. bourbon_scotch

    bourbon_scotch Veteran Member Lifetime Gold Member

    2,019
    52
    Jan 10, 2003
    USA
    Does it do the same thing in neutral or park?
     
  8. Justin79maro

    Justin79maro Veteran Member

    103
    1
    Jan 15, 2015
    Bonne terre, missouri
    It only does it when it's under light excelerarion or when I stall it up. In park or neutral it does perfect like it should
     
  9. bourbon_scotch

    bourbon_scotch Veteran Member Lifetime Gold Member

    2,019
    52
    Jan 10, 2003
    USA
    Do you have a vacuum advance on your distibutor?
     
  10. Justin79maro

    Justin79maro Veteran Member

    103
    1
    Jan 15, 2015
    Bonne terre, missouri
    Yeah
     

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