Idle too fast

351w-holley 4v 650 vac. seconds-9.0:1 comp.-C4 trans.
My idle is running about 150 rpm too fast and the idle screw is all the way out, the choke is open and stuff like that. Timming is at 6* btc w/ vac off 24* w/vac on and its wants more advance than that, but will idle way to high if I do. Normally when you introduce a vacuum leak a engine runs rough but mine gets smoother. Ilde screws are adjusted right. Any thoughts ........[img]/phpBB/images/smiles/icon_confused.gif[/img]

HI 67
I would start by checking for a vacuum leak, use eather a carb cleaner or I have heard propain torch (unlit of course). If the idle changes theres your leak. also check and see that the fast idle screw is off the choke cam. check to see that the secondairs are closed all the way. OH [img]/phpBB/images/smiles/icon_eek.gif[/img] just though un hook the throtal cable maybe it too short not letting the throtal close all the way.. that could be it.
hope this helps
Tim[img]/phpBB/images/smiles/icon_spin.gif[/img]
[addsig]

Back off the secondary set screw about 1/8~1/4 turn and see how it acts.

Does the Holley have two small holes drilled in the primary throttle blades? If so, you need to get replacement primary throttle blades that do not have the holed in them. Have you checked for a vacuum leak? I have had previous vacuum leaks where my car idled better; but the performance very obviously fell off with accelleration.

maybe a faulty vacuum advance? i have problems with my girl's vacuum advance part on her dizzy on a 66 6cyl. the vacuum advance pretty much stayed pulled, like it does when the motor is reved up. and the idle would change and change and change. one minute it'll idle right, then the next it'll idle super low, then it'll idle super high. an never ending story. all it was, was the vacuum advance part on the dizzy.

just my guess what it could be and can be.

Thanks
pedal2themetal45 - Cable is fine, fast idle screw is off the choke cam, secondairs are closed
anthonydalrymple - No holes in the plates
XolieX - she may have had a 'duel vacuum advance' it has two vac lines, one to advance and one to retard. Mine works fine

In addition to what everybody already suggested;

too much initial timing?
gas leaking into the carb from the floats too high?
a somewhat blown power valve? It can stretch and not be completely blown and it will let some gas into the engine at idle.

It could still be a vacuum leak. Some of those are hard to track down. If you put your hand somewhat over the primaries at idle and it runs up its getting too much air from somewhere it shouldn't. Otherwise, doing that should choke down the motor.


[addsig]

Some Holleys have a 2nd throttle blade adjustment on the PS under the VS diaphram. It is only accessible if you remove the carb and then turn the screw to allow the primary blades to close all the way.

Floats adj correctly, timming is about right for cam. How is the power valve tested. Manifold vacuum is 19 inches at idle. I will check for a vac leak and get back with my findings, but any time I've had vac leaks the engine idles like sh_t.

no, she has a single one.