@FWJ posted:@panteradoug I don’t get this point?
You can only increase the amount of fuel at idle which by design won't change th a/f idle ratio.
Why should it not change the A/F ratio when fuel amount is increased?
I don't know precisely but to increase idle speed you are opening the throttle plates and not changing the idle circuit.
The idle circuit in the 4180's is a revised design from the 4150/60's.
In a 4150/60, you can set the idle set screws in the metering block and richen the a/f but in the 4180 that is locked out.
The 4180 idle circuit is much like the Weber 48ida's in that you have in essence an air jet and a fuel jet that you cannot change. The idle screws only react within a 1/4 turn or so and it doesn't change the a/f ration of the "jets" it just increases or decreases the amount of fuel being fed to the intake manifold.
It is different thinking from Holley and you need to work with the 4180's to get the picture. It is a bit brain twisting initially.
The explanation to me was that there is a fine to the auto manufacturer of $25,000 per vehicle that when tested if the emissions results do not comply with the US Federal mandates the fine will be levied.
So Holley designed an idle system that can not be changed to modify idle a/f ratio. This is probably the biggest reason that the Holley carbs on the Mustang GT's were only used for one year before going to EFI.
Those would be the largest risk for Ford v. the 351w trucks that were using essentially the same carbs but with different production list numbers.
That was a project that I did with the 347 that I built 10 years ago and built it with a 2x4 induction system.
The 4180's were not on for long as I found the regular Holleys much easier to understand and tune.
I just point this out as a possible tool to use in identifying the "culprit" in why plugs may be fouling. I have never seen spark plugs that clean again...ever.