Trouble is with a Holley 4150 HP 750 cfm w/vac 2nds on a mild 440. Motor has been sitting for about a year, I replaced the plugs and wires, power valve, needle and seat assemblies, checked float levels and verified spark. Plugs are black as coal and doesn't want to idle. Ideas would be greatly appreciated.

Everyone who said power valve raise your hand .

I pulled it apart again to swap in another power valve, noticed a piece of gasket left from the old PV and it wasn't as tight as it could be. I stripped it al down and soaked in a new can of chem-dip and put it all together cleaner and more carefully this time.

Fired right up, idle fell right in place and tweaked the timing right in. You folks are the best

Ignition timing/initial advance

More or less?

vacuum leak?

What's it got now?

Well I'm not sure if I can believe my light, it says about 30 degrees, won't run with much less. Its a 6-AL2 ignition and the instructions say not to use a dial back light...

It ran OK a year ago when it was parked with no changes since then. I'm assuming the fuel psi ain't too high & the PV ain't blown. What's your idle speed? It's showing 30 initial? On ported or manifold vacuum? I'd want the initial at ~15. Find out what's wonky with the timing reading. Holler back when you can

Is it dribbling fuel out of the shooters? Are the air bleeds plugged? Does it respond to idle mixture adjustments? Is the choke opening properly?
A vacuum leak would lean it out.
12-18 degrees initial (vac adv unplugged) is a ballpark.
I assume no varmints have made a home in the air cleaner.

Pull the carb and give it a detailed cleaning. Corn gas will crust up and make bad things happen.

It sure seems that it is a power valve problem to me. I used to do mobile service calls and had one in the SeaTac Airpot parking garage with a Rambler V-8 and a Holley. I was able to get the family home by plugging the blown PV with JB weld with the advise that they could only use part throttle to get them home (85 miles)and then have the PV replaced by their local mechanic. I would try a PV plug and see if that cleans up the idle. Couldn't hurt to try.

Mechanical advance only MSD pro billet distributor, I set for 25 on the plate and 13 initial and had to advance the heck out of it to get it to run at all. Same mechanical pump, I ran carb cleaner thru the air bleeds. Has four corner idle all closed runs best...weird, I,m about ready to send it to the crusher

could be the coil, or MSD rusted inside.

sure sounds like a bad power valve did you get the gasket in tight??

got another to try.

I've seen the block to main body gaskets do the rich thing too.

Do you have a good running carb to borrow and swap on.

Do you still run the ballast resistor if so run a double male spade to join the wires.

you put fresh fuel in?

I once bought a 3 barrel they said many different carb experts looked at and it runs pig rich.

so i paid 80 buck for it telling my buddy I was sure it was the power valve.

And it was piece of gasket material stuck in it.

problem solved ran good sold it a couple years later for $150.

wish I still had it to play with.

I do have another power valve to try, I will pull it off tomorrow and swap the PV and soak it and scrub it and hit it with air and see what happens. Had to walk away fro it for today , I really appreciate all the inputs.

Assuming the throttle blades are closed down normally to where you are on the idle circuit if you then screw in the idle mixture screws all the way & it keeps idling then the PV is blown (the idle circuit is getting fed improperly from the PV)

And it was??

I think the power valve was leaking.

Glad it's fixed!