Holley 4160 adjustment

[Jims68]

OK... on my Roadrunner I have a Holley 4160 4bbl vacuum secondaries. I have a couple questions. My spark plugs looked really black and not the normal color. I DID go for a nice 40 mile cruise the other night and it runs really good, but I have not pulled any plugs out to re-check them.

So...

1. It smells so rich even after the choke is fully open. Do I turn the mixture screws OUT or IN?? They have these plastic caps that look like screws. Do they pop off? OR just turn the cap? It seems that I've turned the cap before... but it's been YEARS!

2. Also, will adjusting those mixture screws effect any gas "Cruise" gas mileage-MPG? OR are they just for idle?

[swptln]

The screws are just idle mixture adjustments. Doesn't effect the main jets or circuit while driving/off idle. If it was driveable, most likely your float adjustments are too high, idle screws and or jetting is too fat. Turn in to lean, out to richen.
Just because your plugs are black.........you have to read them a little better than just being black.

[Jims68]

Thanks Mark... I wasn't sure which way to turn them. As for my plugs being black... that was just a "quick" look and not really a "read" of them. I may pull a couple out and have a GOOD look at them. It's VERY possible that the plugs were that way because I had not really had it out for a good drive and they were just getting fouled up due to lack of the engine being really warmed up.

I was wondering if the mixture screws had anything to do with normal driving. Oh well... it's possible I knew this years ago, but a lot of that stuff in my memory is gone now!

[Jims68]

UPDATE: I pulled out 3 plugs today and they are just as good after my 40 mile ride as they were after I cleaned them just before my ride. So... I am going to go out on a limb and say that the plugs were black because the last couple of times I had it running, I didn't let it warm up fully and just let it idle in my yard. I know, I know.... I should DRIVE it and get it good and hot. Oh well...