holley carb adjustment question

I just recently installed a used holley 390 cfm 4 bbl with an offenhauser manifold on my 77 258.  This carb was on a car I had before, and never had any problems with it.  When I first had it running over this past weekend, I was able to adjust the idle speed to about 800 rpm.  This evening, when I first started it up to adjust the timing, I noticed that it idled a little high (about 1200 rpm), and it seemed to hang up a little at a higher rpm (about 1500).  The timing was set at about 6-8 deg btdc.  I couldn't adjust the idle down any further, so I went ahead and played around with the timing.  With the distributor plugged, and the timing adjusted to 12 deg btdc, the minimum idle is 1000 rpm.  I was able to get it down to about 800-900 rom if I adjusted the timing to about 2 deg.  I didn't run the car long, but I checked and the choke appeared to be fully open.  Any help about what I am missing/need to do would really be appreciated.

Thanks,
Dan

How about a vacuum leak? that can do it...........
Is something (besides the fast idle cam) holding the throttle butterflies or shaft?

Alright.  I checked the car tonight.  I snugged down the carb and maifold bolts.  A couple where a little loose, but I'm not sure if they were loose enought to develop a vacuum leak.  I then checked the fast idle cam.  It was loose and in the down position, which is off fast idle, right?  The thing that really has me stumped is that the car idled fine on Saturday.  Then, when I started it up on Monday, I started having this problem.  I tried playing around with the idle mixture screws tonight, and got some sucess, but the car seemed to idle a little rougher, so I set them back to where they were to begin with.  The other thing I can't figure out is why the idle seems to hang up at a higher rpm when I hit the gas.  I have to punch it a couple of times before the idle drops back down to about 1000 rpm.  One thing that I forgot to mention last night (because I forgot about it) is that the throttle holes in the carb-to-manifold gasket that I used seemed a little big.  I used a gasket for carbs with a 1 11/16" bore, but I think that the 390 has smaller bores?  Would this cause the problem?  Also, I always thought that a vacuum leak would prevent the car from idling properly if at all.  While I can't get the idle down, it idles fine.  Since I've never had this problem, how do I go about finding a vacuum leak?  Thanks again for all the help.

I checked the throttle cable and there is some slack in it, so I don't think that it is holding up the throttle.  I started the car today, and after I got it warmed up a little, I tried spraying carb spray around the mainfold mating surfaces.  The idle improved a little when I sprayed the runners to the the #5 and 6 cylinders.  Next, I placed a rag over the carb to see what would happen.  When I covered the carb, it died.  I did this since a member on the other board said that if this occurs, then I don't have a vacuum leak.  Since these 2 tests kind of contradict each other, I don't know what to do next.  Anybody got any suggestions?  PMM, I want to take you up on your offer.  Let me know when it is good for you, and I can come by, or you can come over to my place if it is easier for you.  You can send me a pm if you like.

Thanks for all the help guys.  PMM came by and looked at the car.  He snuck(sp) up on the carb and it did improve the idle.  I was just stuffing the rag in the carb and that's what was killing it.  He did agree that there is a leak around #5/6, so I need to fix it.  Thanks again for all the help, and to Ron for coming out to give me a hand.

Dan