Tuning by float level?

Discussion in 'The Venerable Q-Jet' started by Electra Sweden, Mar 15, 2023 at 7:44 AM.

  1. Electra Sweden

    Electra Sweden Well-Known Member

    So there is quiet a lot of information online on how to tune-up the Quadrajet by changing the primary and secondary nozzles and metering rods, as well modifying the sizes of certain passages.

    However, I have found none on what to do with the float level. As far as I know for instance all Buick 455 1970 had identical Quadrajets apart from the individual tunings and the part number corresponding to that. As basically every engine model has individual float level specs this must be a tuning parameter of some sort. So how to go about the float level when custom tuning a Quadrajet? If the carburetor is already tweaked, it sounds unreasonable that the float level should be left at the stock level. Trying to asses the overall air fuel ratio and adjust the float level only if it is lean or rich in general? Reasonably, a higher float level would result in a richer mixture overall and vice versa?

    BQUICK Gold Level Contributor

    As far as I know the quadrajet is designed to run at a set float level.
    That said an easy way to raise or lower it is with fuel pressure. On my Holley Dominator for racing I run more fuel pressure (like 8.5psi) to raise float on good air days for slightly richer mixture and less on hot humid ones when I might set it as low as 5.5. But...Holley has 2 bowls so maybe more effect.
  3. CJay

    CJay Supercar owner Staff Member

    I would go by the casting number on the carb and set it for that. Float level isn't going to make any difference in performance on your Electra. This isn't a max performance racing application.

    I'd be more concerned about air fuel readings at idle and cruise
    2.5 likes this.
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Max Damage likes this.
  5. Electra Sweden

    Electra Sweden Well-Known Member

    That was a neat trick to tune this!

    It got enough power but the current MPG bothers me. Best MPG I had for a longer trip last year was 11 and I know many people get a lot better than that on these engines.

    Hmm. Should maybe buy that book. Have you read this one btw? https://www.amazon.com/Quadrajet-MPG-Secret-Second-system/dp/1075307716

    Still not entirely convinced though that the fuel pressure and needle seats are the only parameters of importance when setting the float height. Looking through the chassis service manual, all 350 engines had a float height of 5/16" and the 455 3/8". Except for the Riviera, all these engine variations had the same fuel pump and similar operating RPMs. And reasonably the same needles and seats in the carburetor, as well as similar fuel feed paths? If Buick then still bothered to go through the trouble of having different float heights already 1970, there must be something more to it?

  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Nope, never saw that one.

    OK, let us know what you come up with.:)

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