I'm using a holley 4000 carb on my 53 Ford Customline with a 255 Merc flathead. I know it's not y block but the carb is. Anyways I have a massive hesitation. The carb doesn't transition between idle and higher rpms very well. It does get a good shot of gas when pumped, but I just can't get this one to run right and when I first put it on it ran really well. I figured someone must know these carbs really well so I thought I'd ask.

The best answer for you question would be go to search on this site and type in teapot you will have probably over 13 pages of info.

It sounds like you may have too low a float setting, however the search result will give you several hours of good reading and good advice on trouble shooting this carb.

Here is a link to some info.
http://www.y-blocksforever.com/forums/Topic53385-3-1.aspx

marv

Fresh carb kit?  Top cover gasket in good condition?  You might try using a fibre washer on the center bolt on the top cover to insure there’s not a vacuum leak right there.  A vacuum leak at that point will keep the power valve from working as intended.  Load-O-Matic distributor?  If so, is it advancing correctly when checking with a timing light?  Also check that the pair of air bleeds located close to center carb stud on the top cover are clean and/or clear.  Shooting some carb cleaner into these with the engine running should indicate if these passages are clear or not.

Lorena, Texas (South of Waco)

Okay, so I made one big change, I put a different bowl on this carb to see if that would make a difference, and it did, well after it warmed up it did. I think a decent choke would cure the rest of the problem. When it was cold it now hesitates and pops back at me, after it warmed up a bit it quit doing it. I had this cool manual choke set up on it, but I lost the little arm that controls the choke lever, and it's what the wire pushes and pulls on. I'll have to see if I can make another I guess. the only part that was fresh was the power valve assembly. I need to run the old gas out and put in some new that may help as well as the gas is a couple years old. It's ridiculous how gas doesn't keep very well anymore.