Carb tuning
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Carb tuning

  1. #1
    Junior Member
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    Default Carb tuning

    Ok boys I have a 477 BBC with cast iron rectangle port hi-performance gm heads. Pretty mild motor 4" stroke, 6.135 rods with flat top forged pistons. The compression ratio comes up to about 8.25:1 on the engine. The cam is a crane 168731. So it has a b&m 250 blower and super chiller intercooler on top running about 8psi boost. The issue I have is the idling of the boat and when shifting into gear, the engine is constantly surging at idle and in gear. This is a Dean Nickerson carb but it wasn't originally set up for my engine. So if I wanna fix these issues myself what's the best route to go? Carb is a 1050 dominator set up with 96 jets all the way around and has 3.5PV in front and rear. Carb is also not boost referenced.

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  3. #2
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    Yes I have tried adjusting the idle circuit screws on the metering blocks togethere and separately with no success.

  4. #3
    Senior Member earlbrown's Avatar
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    And have those carbs been ran on top of a blower successfully before without being boost referenced? When you run the idle screws all the way in, does the engine die?

    I'm not a roots guy but why powervalves on both sides and why aren't they boost referenced?

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  6. #4
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    It's a single carb and yes it been on top of a blower before. Don't know exactly why or how Nickerson sets up carbs. All I know is the issue I'm having and it was supposed to have ran on the boat before I got it. No engine won't idle with screws all the way in

  7. #5
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    Default P/Valves???

    I'm somewhat confused here..... Why would you have P/valves in a carb that is boosted to 8 PSI??? Those 3.5 PVs quite likely, never open..... Is there a "turbo lag" with a roots type blower? ( I have ZERO experience with a carb on a blower) (But, I'll sell you a nice Enderle Hat!!!)

    As far as the "surge", it is a vacuum/pressure cycle reaction.... There are people that spend thousands to get their engine to "surge"..... I've known v drivers that use the "down side" of the surge to slide the v drive cleanly into gear.....
    Ray
    LOUD BOATS SAVE LIVES

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