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Re: Exhaust bang bang bang [message #366787 is a reply to message #366771] Wed, 15 September 2021 08:18 Go to previous messageGo to previous message
JohnL455 is currently offline  JohnL455   United States
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
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Senior Member
Larry, idle mixture setting is a bit like tuning a guitar. Instead of a strobe tuner you use a tach needle. Since we have divided manifolds, each idle mixture screw feeds 4 cylinders discretely. They don’t blend like with an open plane racing manifold. With engine at full 195 temp you slowly adjust each mixture screw to get maximum idle speed. Each screw is only contributing to 4 cyls so it’s a bit of a back and forth process. If they were set wrong, you will have to go and adjust the idle speed screw to get it to 650 so you are in the idle circuit range. The screws only work in a limited range. Never bottom them with any force, and opening past about 3 turns does nothing further. Once you find the max RPM center spot about an 1/8 turn range, stop there. Then turn each screw in very slightly to where it would just want to start losing RPM but does not. You are then at the best lean edge of the best range. The GM lean drop setting would mean then turn one screw in watching tach to lose 25 RPM. Then turn in other screw for a 25 RPM drop. Then go back to the speed scree and add the 50 RPM you lost to get back to the 650. Technically this should be done with the air cleaner in place and the AutoThermAC pre heat active so carb idle air is in the 117F range, but you need to have a flexible carb mixture tool to do it correctly. If your carb throttle shaft is worn as Jim H suggests could be, you will be adjusting to a moving target making it less accurate.

John Lebetski
Woodstock, IL
77 Eleganza II

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