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4180C Idle Mixture Setting Procedure?


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Interestingly my emission label simply says US EPA for 1986 model year heavy-duty vehicles, no reference to 49 state or non-California.

AllData shows 2 different vacuum and vapor hose diagrams, one CA specific and one except CA, they are not easy to read being a black and white snake's nest of vacuum lines and vent hoses.

 

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Interestingly my emission label simply says US EPA for 1986 model year heavy-duty vehicles, no reference to 49 state or non-California.

AllData shows 2 different vacuum and vapor hose diagrams, one CA specific and one except CA, they are not easy to read being a black and white snake's nest of vacuum lines and vent hoses.

You adjust the idle mixture just like you do with any Holley carburetor. You need a warm engine, a screwdriver and a vacuum gauge if you really want to be finicky. You ready?

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You adjust the idle mixture just like you do with any Holley carburetor. You need a warm engine, a screwdriver and a vacuum gauge if you really want to be finicky. You ready?

I may remembering wrong, but I believe these are small Allen head (they are in the throttle body, 4 of them) and are a royal PITA to get to on a 460.

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You adjust the idle mixture just like you do with any Holley carburetor. You need a warm engine, a screwdriver and a vacuum gauge if you really want to be finicky. You ready?

Changing plugs, wires, cap, rotor, pcv, coil, air filter (and compression test) while I'm at it, today. Gonna adjust the carb next week.

Trying to hunt down accurate idle mixture procedure ahead of adjustment next week.

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Thought so. In that case you can't just adjust for max vacuum. That's why they introduced the propane method.

It is really confusing that they say the trucks above 8500 lbs don't use the propane method, but then they don't give the proper method.

Bill - Is there a rule of thumb? Like "Find max vacuum and then lean the mix by 1 turn"?

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