Rebuilt 440, mild roller cam, roller rockers, brand new Holley 750 vacuum secondary, no PS or PB, Cant get it to idle smooth as it should be. Idle smells rich, have to change my clothes after a ride.
Vacuum gauge reads only 10psi at idle - this is the vacuum from the back of the carb to the PVC valve on the driver side valve cover. (shouldnt it be more like 15-20?)
If I unplug this hose from the vacuum gauge and partially cover up that hose with my finger, the engine will speed up (bad?). If I take my finger away, the engine will stall (good?).
I have a litle bit of crankcase vapor smoke coming out the breather on the passenger side valve cover which indicates a positive pressure not a vacuum there. (bad?)
If I cover the carb with my hand the engine does not speed up and will stall out. (good?)
thanks for your advice.

Sounds like the rings haven't yet seated? Did you degree the cam or just match the dots? IIRC, and it's been a LONG time, Holley's come with a 12.5 HG power valve and you're only pulling 10 HG? So the PV is open the entire time you're idling?

has holley changed? used to all be 6.5's. BTW I have b-tt load of new ones LOL

I think I removed my 6 barrel setup in the early '80's? I'm just not sure anymore. My memory for details like that is failing.

But isn't the PV the usual culprit for rich idle mixtures?

PV enriches the mains only, not the idle circuit. Doesn't matter if it's open at idle or not.
My 451 idles at 8" Hg and the idle AFR and RPM stay the same whether I have a 10.5 or 7.5 PV.

Incidentally there's another urban legend, which Holley is still perpetuating, that your PV should be 2" below idle vacuum. Which is pure bull. You want it to be several inches below cruise vacuum - the exact point has to be determined by experiment and a wide-band AFR meter to assist.

My cruise vacuum is 14-15", and I'm still trying to decide whether the 7.5 or 8.5 feels better on the butt-dyno. I tried a 10.5 but it was coming in too early, just making things overrich. Remember you want the mixture to go leaner at part-throttle, until somewhere above 50% of max power (this point on the curve is different for every engine and induction system).

I've seen many motors with Holley carbs that were idling on the transition circuit( the small rectangular slot that should be above primary throttle blades at idle RPM ) which will open the power valves if the idle vacuum is below the power valve opening vacuum rating which makes the idle mixture very rich

I was only responding to the guy who thought that a PV opening at idle vacuum would cause trouble.
If the OP's carbs are well into the transition slot, that has to be fixed first anyway!

I believe the books I've read said the lower portion of the slot (.020 or so) can be exposed without ill effect ?

You are right, Holley says you should have a little bit of transfer slot showing at idle. So for all you guys out there with a mild or stock cam, how much vacuum are you pulling at idle? thanks

470" low deck,10.2:1, Comp XR280R (242/248@.050)solid roller pulls 10-12" and idles nicely at 900 rpm with a Holley 800 DP that's essentially untouched.

Pretty sure that cam isn't "mild or stock".

My 51 pulls 20" at idle, bone stock. But's it's a flathead six and just about as relevant.

What is your timing at idle? Do you vacuum advance or mechanical? Check the gasket under the pv to make sure it was installed correctly. Check the gaskets under the carb for good seal.

Me thinks the books you read are wrong, no slit visible works the best for me
My old 517 C.I. pump gas stroker 400 motor with a low deck six pack on it would idle at 850 RPM in gear with 4.5 inches of vacuum with a 3.5 power valve
thhat motor had 9.25 to 1 comp ratio with slightly ported 906 heads with bigger valves and custom grind Comp Cams solid roller that was 260 degrees @.050 on the intake with 1.6 rocker ratio with .700 net lift at the valves
I learn many things with that car and motor, especially on the tuning of the carbs
Test, test and then test some more until you disappear in a blinding flash as exceed light speed
Try it and see if that will work for you also

No transfer slot visible means the t-slot isn't flowing at idle. So it'll take time to get flowing as you crack open the throttle. This results in an off-idle sag or stumble. You can partially cover it up with enough pump squirt. I suppose with a loose enough converter it won't be noticeable either. It definitely is with a four-speed and a lot of cam.

Also, with any kind of bigger cam, there may not be enough air coming through with the throttles closed that far. You can also cover that up by cracking the secondaries...

Of course if all you're interested in is idle and WOT on the strip, it's no problem! But there's a lot more tuning involved to have good tip-in and cruise manners on the street. May I recommend the RFS Holley forum.