Holley 4150 750...recommendation to go 650

Discussion in 'Troubleshooting & Diagnosis' started by JD Z, Oct 27, 2017.

  1. JD Z

    JD Z Veteran Member

    I have a 4150-750 on the car. It’s an 80Z with an updated Cam, though I don’t know a lot about the car just yet. Other than the Cam has caused me low vacuum issues. I’ve taken it into a shop a few times for miscellaneous things like timing, brake lines, tranny oil change, etc. I went to pick it up tonight and it started real hard. I had to pump it quite a bit to get it to go. The owner came out and said it’s a bit cold out here (45 degrees) and your 750 doesn’t have a choke. He told me to pump it good when it’s cold and he suggested I may want to consider updating to a Holley 650 with electric choke. He said the carb is too big.

    Any thoughts on issues with going to a 650? Not sure why the previous owner went for a 750. The carb codes are 4779-7 and 1800.
  2. JD Z

    JD Z Veteran Member

    And, less than two tanks of gas and the mileage is terrible at best and there is a smell of fuel regularly. If that helps any on the recommendation. It’s been 30 years since I had an 80Z but I don’t think I put that much fuel in it.
  3. SRGN

    SRGN Veteran Member

    Feb 20, 2009
    Central NJ
    Carb may need a rebuild, but I don't think its too far off on size. Biggest issue is that it is a mechanical secondary carb, for a car that sees primarily street use I'd recommend a vacuum secondary carb with electric choke.
    JD Z likes this.
  4. JD Z

    JD Z Veteran Member

    It will be a mainly a street cruising car with the desire to be able to get up and go for sure. Not racing or drag. It will get less than 1,000 miles per year on it likely. The carb date code suggests year 2000 and it was said to have only 2,000 miles since it’s rebuild. Not sure if that rebuild included this carb.

    It’s a 4speed with 373 rear. Really short 1st, 2nd and 3rd for that matter. It doesn’t take long at all to get to 4th.

    Any issues dropping to 650? And what should I consider in terms of vacuum secondary, double pumper, etc. I’m a novice so just looking for feedback before I talk with the tech.
    Last edited: Oct 27, 2017
  5. 71flh

    71flh Veteran Member

    Jun 1, 2010
    Holley recommends a 650 and I recall doing some VE calculations that supported that. Then again I've long since forgotten the equasion and values used in the calculations. :)
    That said, lots of people feel that a 750 is better for a performance applications, particularly in a light, manual trans car, which may not describe a an 80 Camaro.
    I'd probably check the plugs for running rich and maybe tune the carb, as well as see if it needs cleaned since if it sat, today's bad gas rots things.
    JD Z likes this.
  6. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

    well, if its over cammed (vacuum issues) it certainly might be over carb'd.

    problem is you dont really know what the engine specs are - cam, heads, etc. so its hard to make any recommendation. I always think its better to err on the small side for carbs on a street car. a choke might be nice. but a 750 could certainly be tuned better. and will you be driving it in the cold much?
  7. Zspoiler

    Zspoiler Veteran Member

    May 6, 2012
    Federal Way, Washington
    Just go with a Holley 3310 750 Vacum secondary carb. They usaully come wit an electric choke .And are easily tune-able.
  8. cadillac_al

    cadillac_al Veteran Member

    Apr 22, 2015
    There is no choke plate at all on your carb? The problem with running without a choke in cold weather is it takes all that extra pumping to get it started that you run the risk of getting fuel in your oil on a regular basis. You should have a choke on any vehicle that will be used below 60 degrees. If yours has no choke then I would stay with a 750
    JD Z likes this.
  9. G72Zed

    G72Zed Veteran Member

    Sep 8, 2015
    I would suggest you get a good vacuum reading at idle and see what it is. You may be under the Power Valve opening point or close to it. With racy cams and lots of intake pulse reversion, it may be triggering the PV to open.
    You should be able to get your 750 dp in tune, a 650 vac or dp not set up right will not run any better.
    JD Z likes this.
  10. JD Z

    JD Z Veteran Member

    I’m in Kansas and I don’t expect that I’ll drive it much in weather below 50. Today its 36 and I did. I believe I need an electric choke as my 750 has no choke. Odd because it lived its life in MA. The mechanic shop just suggested that the 750 is too large for my motor.

    If I go with a Holley 650, what might the concerns be moving from a 750 the previous owner put on? I’ll not be drag racing, though I don’t want to sacrifice an unknown. It feels like a 650 with electric choke would deal with the colder weather when needed, help with the gas mileage, and run better overall. I just want to understand what I’ll be giving up.

    The car does have an updated Cam that contributed to low vacuum, but I solved the vacuum problem with a pump for now.

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