I have a '78 Monaco former CHP unit with the original 440 Magnum which has been rebuilt. It has a small cam in it, unknown grind, Hooker Super Competition headers and an aftermarket dual exhaust system. Stock ignition with a recurve on the distributor.

Recently I have been working the bugs out of it (has not been driven much in a couple of years). Needed a carb for it so I pulled a Holley 750 VS off the shelf I had laying around, along with the intake from a '69 Chrysler 440. Carb was in very nice condition but I put a kit in it due to needle seats getting hard and gaskets drying out.

Works great when you first start it up, but after it warms up a bit at an idle she starts slowly loading up. It is running rich; you can smell it and see the cloud of smoke start forming in the garage.

Like I said before, carb was in good shape internally and had the stock "72" jets in it. This is usually pretty close jetting for any other 440 I have worked on, and that has been over a lot of years. It has a brand new power valve in it. Wet float setting is dead on. I used a Holley rebuild kit. Idle mixture screws don't make much difference when you adjust on them. When you pull the PCV hose, she idles way-y-y up. Altitude is about 2400 feet.

My inclination is to pull the bowls and drop down to about a "68" jet. But before I do, I thought I would see if anybody else has been to this rodeo before, or if I might have missed something.

Ideas? And thanks.

May God bless America,
Paladin

Hmmm...choke operation, power valve Hg too low, blocked air bleed, pulling fuel through booster come to mind. Stick a vacuum gauge on the motor, what's it show for idle vacuum, and is it steady?

Electric choke works fine and is not sticking.

Air bleeds all seemed to be clear, ran some low pressure air through them to double check during the rebuild.

Vacuum gauge holds steady at 18 Hg before it slowly drops to around 15 as the engine loads up. It moves back and forth at around 15 as it continues to load up.

It acts like a power valve, but this is a new Holley kit.

My brother was having issues with his 750vac. secondary loading up at stoplights, turned out to be a hole in one of the floats. New floats in it and it runs great, Might be worth checking

this will certainly bring on some "expert" criticism,but,if it still has the stock,low compression pistons in it,and 452 heads,that 750 is an awlful lot of carb for that engine.
i know,i know,it would have had a thermobog or quadrajunk on it originally,with great big secondaries and a 750 or 850 rating. but,that is with tiny primaries and those big secondaries only in use when she was on the floor. i'm just sayin.....

I thought about the float, also. But I doubt it has a hole in it because the wet setting stays exactly where it should be.

Could be a couple of things.

Check the needle and seat for debris. Change the O ring on the needle and seat with a correct o ring.

If the carb sat, and dried up with old fuel, that could be an issue.

If the car sat a long time, crap from the fuel tank and lines could be creating issues.

You would see fuel dripping from the boosters (front or rear), with any of those issues.

I was going to say that the jets have no effect on idle, cause the blades should be closed...but then you said the idle screws have no effect.

where's the throttle setting? timing?

be sure the throttle blades are not too far open at idle, or the idle screws will never have an effect

LEAKING POWER VALVE

It's not the jetting. I would do the std PV check, when it's good & hot & acting up, turn the mix screws in all the way & see if it does or does not die. EDIT did the carb work fine originally b 4 storage (I'm assuming it did) and the idle mix screws having no effect is that on initial startup or when hot/loading up

If the carb is still on the idle circuit, the PV has no effect at idle.

see,i knew an expert would come to the rescue. good to know,so i guess a stock 318 will sit and idle smoothly,without loading up or black smoking with a 1050 dominator on it

Pull the air bleeds out and run some carb cleaner through. Also check the power valve for tightness, mine was leaking past because it was a tad loose. Between the dirt in the bleeds and leaky powervalve mine ran like doodoo. Now all is well.

If a PV is ruptured or open it will greatly affect idle even if its "idleing" in the idle curcuit, If the idle screws can be closed & it still idles its still getting fuel, You can rule out the needle valves because its holding fuel level, You say its getting 18 inches vacuum, thats very strong & the stock 6.5 PV should not be an issue. Things i would check.

Make sure you have the "right" primary metering block gasket, you said the carb ran fine before, so there shouldn't be any issues with the IFRs being tampered with.

With good vacuum like you have i'm sure the primary throttle is not opened up that much allowing it to get into the main curcuit.

I would double check the PV also, make sure the gasket is in there right. See if the carb is dripping fuel from the base when lifted from the manifold, i'm sure it is.

If for ANY reason the engine spit or kicked back through the carb it can/will take out the PV, especially if the base doesn't have the "blowout" protection check ball installed. BB mopars are notorious for doing this if timing isn't close or you get a lean pop.

Since you put a kit in ,you may have gotten the power valve gasket wedged in and not letting the PV seat properly. Happened after the Stepson opened up his Holley. i noticed the PV was not as close to the metering block as it should be.
The first question to ask when troubleshooting is "what did you work on last?" Gets some strange looks but is a usually a shortcut to the problem
Hope I helped,
Ron