New 350 Hard start, runs rich - suggestions

New 290hp crate motor, have Weiand Dual plane with Holly 750 Vacuum Secondary carb. New MSI HEI dist. Problem: runs rich, poor throttle response. All parts are new. Is oversize carb the problem? Have tuned jets with Vacuum gauge to max vacuum, floods easily.Doesn't have the get up and go I know it should have. Any help appreciated.  

The first step is to either head to the library or the book store and pick up a book on tuning holley carbs.  Lots of great info.  

Aside from that, the first steps I do when bolting on a new carb are to set the initial idle.  The idle speed screw on the drivers side is usually preset to a location that will  not open start the main boosters.  If you start cracking open the idle speed screw and it activates the main boosters then you will idle really rich and the idle mixture screws will not be responsive to adjustments.  I have found that adjusting the angle of the secondary blade to achieve idle while is much more effective.  I usually buy the little secondary idle screw option available from Holley for about $20 and bolt it on for easy adjustments.  With the carb upside down set the main idle speed screw on the drivers side so the little verticle slot alongside the throttle blade is open NO MORE than .040".  With the carb still upside down if you have not purchased a 'quick adjust' secondary screw, you can screw in the little recessed screw that adjusts the secondary brade angle to get more idle speed. reinstall the carb and fire it up.  If it still idles too low then remove and flip the carb and adjust the little secondary screw again to raise the idle.  When you get it to idle at a decent speed and you have still not moved your primary idle speed screw on the drivers side then you are in good shape.
You can now hook up a vacuum gauge and adjust the two idle mixture screws on either side of the carb for highest vacuum before stumbling.  Hopefully this will raise your idle a little and you can drop the idle with the primary idle speed screw now.

Only now will you want to start fooling with jets and squirters.  I have found that the 750 carbs on a generic 350 engine have pretty good jets - a little on the rich side but not much.  The main problem is usually the squirter.  Buy a few different squirters and try them out.  Most of the plain-Jane 350 I have dealt with using a 750 vac like about a 35 squirter.  Try several between 31 and 40 to see what makes the car most responsive.  You will notice a big difference when changing them!  

Thanks for the input. I can't get it started due to the flooding at this time. Once the rain stops here I can start working on the carb. I do have the Haynes Holly Mauual already, and I saw where it discusses the secondary idle adjustment screw. I'll let you know what happens. Thanks again.  

I also have a 350 which starts hard, responds to heavy throttle SLOW, has a tall top end and fouls plugs often.  Sooooooooo.....I replaced the plugs with some hot babies (or you can chunk out the $$ and put those Platinum or four post plugs, etc.).  I also (I think this helped the most) bought a bottle of STP octane booster, any branbd will do.  Now, it starts if I look at it funny, and the throtlle is better but not quite where I want it.  After some research, I found out that I have the wrong intake on.  I have an open plenum and I should have a split one.  I don't know much about these things, I learn by screwing them up, but this has worked great for me.......................er, it worked so well, I blew it up two weeks ago......back to the drawing engine hoist.