Holley 650 stumbles up 3,000 rpm

Discussion in 'Holley' started by Gary lyles, May 22, 2020.

  1. Gary lyles

    Gary lyles Active 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 Active 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.
  7. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    So , did you find figure anything out ?
     
  8. Gary lyles

    Gary lyles Active Member

    It does have a calculated 10:1 compression. Stock converter and I believe it has 2.73 gears, comp cams recommends 3.40-3.70.
     

    Attached Files:

    Last edited: May 29, 2020 at 11:58 PM
  9. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Not the best cam to choose. It's a straight pattern cam, Buick engines like a dual pattern cam with more exhaust duration than intake duration. If you truly do have 10:1 static compression, that cam will give you close to 8.3 Dynamic Compression. That is close to Race Gas territory. Does it ping? I don't say this very often, but you could use a bigger cam. Seems like your problem is a mismatch of parts. You need a bigger carburetor (Q-jet), more converter and more gear.
     
  10. Gary lyles

    Gary lyles Active Member

    Would it be worth it to get the Holley efi system and any recommendations for new gears? And I’ll look into possibly getting a cam from ta performance. It seems to run fine on pump 91 it doesn’t do anything that would make me think it needs race gas, just the problem under WOT
     
  11. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

  12. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    just reread post info .
    "no power/lean before 3000 rpm" . just thinking out loud - that's about the time the secondary's are starting to kick in . so maybe primary side problem ? non functioning power valve , lean ?
    and what carb was on there originally , that was running good ?
     
  13. Gary lyles

    Gary lyles Active Member

    It was the original Rochester carb but that was also with the stock motor before it was rebuilt, I’m going to have my motor guy check it before I think about buying a new carb
     
  14. Gary lyles

    Gary lyles Active Member

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