hunting idle

[Marx3]

Hi, I rebuild a 17085227 for my buddy.
Problem is that it idles poorly...
Engine is a stock 1971 Buick 455 in a Riviera.
Heads are machined so CR is about 9.5:1, cam is

•Advertised Duration (Int/Exh): 262/268
•Duration @ .050 (Int/Exh): 219/227
•Gross Valve Lift (Int/Exh): .484/.505
•LSA/ICL: 112/108


bypass air:
Tube: 038
DCR: 052
lower idle bleed: 076
upper idle bleed: 069

main airbleeds( single ): 085
jets: 77
rods: 50M

I have a wideband and we dialed the AFR in to about 14.5:1 and 12.8:1
Car drives and pulls like it's fuelinjected. Flawless response etc, but the idle is not as good at it could be I feel.

If i stick my finger down the primary bore to cover the airbleed inlet up top the airhorn idle rises alot and smooths out.
The mixture screws dont have much control over the idle.

Which values should the idle system have?

[Marx3]

Sorry. THESE are the correct cam specs

Advertised Duration (Int/Exh): 268/276
Duration @ .050 (Int/Exh): 227/233
Gross Valve Lift (Int/Exh): .505/.521
LSA/ICL: 110/106

[Shark Racer]

Where is the car at 14.5 and 12.8?

12.8 WOT and 14.5 cruise is good. 14.5 idle generally won't work, you need to go a bit richer or the car will start to miss.

[Marx3]

14.5 at cruise and 12.8 at wot ofcourse.
I can't measure idle afr since my o2 sensor won't go deep enough in the tailpipe.
closing the choke plate the slightest causes idle to rise considerably and smooth out.
Should I open up the dcr a little? I haven't written down what size the air bypass is, so don't know right now.
I am going over to his place later today to take the carb apart and measure.
That's why I would like to know what bypass, tube and dcr should be?
It seems to get too much air in idle.

[TommyK]

Maybe just back out the mixture screws and see if that improves things.

That is a VooDoo cam yes? I run the same cam in a 460. It will have a little lope to it.

[Marx3]

The mixture screws have little to no effect on idle quality.

I have rebuild and adjusted many Qjets, I know how to do it.
I just need to know what size tube, DCR and bypass would fit this engine good.
And yes, it's a cam with some lope in it:-)

[Cliff Ruggles]

I'd close down the lower IAB to .059", and it should be fine everyplace.  Otherwise, it's wanting more idle tube and/or larger idle down channel restrictions.  The 110LSA is the biggest problem, increases overlap and degrades idle quality, so the engine wants larger passages in the carb to get the idle fuel that it needs....Cliff

[Marx3]

Well I am not the biggest fan of lope and miserable idle:-) actually my buddy is also kind of tired of the cam. The powerband is a little misplaced in the "low" compression engine. Mileage is completely destroyed! 110 LSA/268 duration and 8.5:1 SCR be damned!
I will check up on the IAB!
Thanks alot to you all three.:-)