Holley 650 stumbles up 3,000 rpm

Discussion in 'Holley' started by Gary lyles, May 22, 2020 at 3:02 PM.

  1. Gary lyles

    Gary lyles Member

    I have a Holley 650 on my Buick 350. In WOT it seems like it’s running very lean until about 3k rpms. Before I got the motor rebuilt and this new carb it would do a burn out no problem but now it struggles to make any power before 3k rpm
     
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    What else was done to the motor during the rebuild? Holley 650? Vacuum secondaries?
     
  3. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    Have you measured vacuum at idle? Whats the power valve?
     
  4. Gary lyles

    Gary lyles Member

    It has a Ta sp3 intake, comp cam, 10 to 1 compression, and headers. It’s the Holley 650 brawler with vacuum secondaries.
     
  5. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    should be a quick fuel #BR67207 ? that's got a 6.5 p/valve , 68 front jets and 31 pump nozzle according to summit info .
    first thing is you will hear you need a bigger cfm double pump carb . bigger yes , 750-850 ? I have good luck with the vac secondary carbs . that should have the adjustable vac secondary correct . be sure you review/understand the instructions for that and test drive before making adjustments . that comes preset with a purple vac sec spring I believe . I've run a couple - never had to adjust , run fine . jet size etc looks pretty good , not too lean .
    but , if it ran ok before engine work - - - - - ? also new engine combo = adjustments needed probably .
    2 cents .
     
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Did the machine shop tell you that the engine has a calculated 10:1 compression, or did you just use pistons rated at 10:1, and assumed that the compression was 10:1? It might not be.

    What comp cam? What are the specs? You might have over cammed the engine. The carburetor is undersized at 650 CFM. In addition, the Holley vacuum secondary carburetors are not as good as the double pumpers. Are the rear gears and torque converter appropriate for the cam? You will also lose some low end torque from the single plane intake.

    You may have a mismatch of parts. Lots of questions.
     
    GS464 likes this.

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