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Old 10-19-2019, 07:20 PM
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DeeVeeEight DeeVeeEight is offline
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Default Holley 4150 troubleshoot and tune questions

Holley 4150 750 CFM tuning questions. I rebuilt the carburetor last week. During disassembly I found that the secondary power valve has a plug installed. My primary jets are 71's and the secondaries are 80's (mechanical secondaries). After rebuilding and tuning I found that the idle mixture screws have an uneven effect on the vacuum reading (max vacuum is approximately 15 inches). Is this because the jets are so rich? The engine runs smooth at idle and is fairly smooth in response throughout the range, though there is a slight hesitation when opening up the secondaries - which I am hoping to fine tune and eliminate. Your thoughts? The engine is a fresh 355 with a mild cam, 9 to 1 compression.
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Old 10-20-2019, 06:45 PM
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Twin_Turbo Twin_Turbo is offline
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Did you use a 7.5 pv? Transfer slots squared? Pv linkage adjusted correctly?
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Old 11-30-2019, 11:59 PM
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DeeVeeEight DeeVeeEight is offline
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Some internet research shows that the carburetor I have is set up like this from the factory. I switched to full intake manifold vacuum for the vac advance and tuned the carb some more - all is well. Initially the throttle plates were over adjusted with the idle screw and I was bypassing the idle circuit.
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