been working on my car pretty hard for the past few weeks but im starting to feel like im trying to tune my carb around a vacuum leak.even with my loose 4000 stall the idle drop 500-600 rpm in gear,then slowly gets lower until it dies.i know its in the carb now since i rebuilt a buddies 750 and it worked and ran so much better on my car.i seem the have a vacuum leak around the throttle shafts,even though they feel real tight.i know its not the booster or intake leaks since other carb runs fine,plus ive plugged every port on intake and carb for now.timing is 18 initial 36 total...i knew i shoulda went for a new carb instead of reman.....anyone ever experience anything like this?thanks for all the help getting me ready for the next track time....

What kind of carb? If it is a Quadrajet, and you have a leak around the throttle shaft, most likely the body of the carb wore instead of the shaft. The shafts are steel, and the body is aluminum. You know which one will wear out first.
You can check easily by removing the springs and linkage from the throttle so it moves freely. Then, rock it back and forth and see if there is any sideways slack. If there is, most likely it will be the carb body, and you can repair that by disassembling the carb, drilling the throttle shaft holes larger, inserting a brass "valve guide" type sleeve into it, and putting it back together. You will need to carefully ream and polish the guide so you have perfectly free movement in the shaft again. That fixes most worn out Quadrajet shafts.

its a holley 750 DP..like i said no movement at all but its the only place where it seems i can have a vacuum leak when i spray it down with starting fluid.is there any chance a 750 VS baseplate will work temprarily to establish whether or not this is the prob?(besides linkages and such)

I've never seen a throttle shaft vacuum leak so bad it would kill an engine. If anything it'll give you a high/slightly rough idle and you might have to open up the idle mixture screws a little to compensate but that's about it.

Chances are there's other problems inside the carb that are the real reason for the situation.

Yes, I beleive you can use a VS baseplate on a DP, linkages notwithstanding. You'll have to make sure something is holding the secondaries closed (besides just engine vacuum) but I believe all the vacuum/idle passages and such are the same down there across most models.

Easy to lay them side-by-side and compare passage for passage before you make your final decision.

Holley has a loose linkage new from the factory. I'm with Damon on this, it's something else. Holleys are famous for shrinking and leaking metering block gaskets. I'd snag a set of the blue or red reuseable no stick gaskets and a can or 2 of carb cleaner. Blow that sucker out then put it back together. Also look real good at the air bleeds. They are very small on a Holley and block easily.

Are you possibly using a carb spacer? There was a post quite a while back (by Marv Davis I believe) about checking spacers against a piece of glass to be certain they aren't warped of cast wrong. The person had similar problems as you. Any starting fluid sprayed at the throttle shafts would run down to the spacer, giving a false indication. It's a long shot, but check it out. Check the baseplate against a piece of glass too!