Why is my car so painfully slow? I have no power on tap.

Ive read that Y blocks are pretty darn tasty and quick off the mark.

My Mercury has a 2 barrell intake with Holley 2 barrel carb. Is this the reason?

If I stamp my foot on the gas, I get a major flat spot as it seems the carb starves the engine of the fuel required for any decent acceleration.

The carb has been fully rebuilt. Would a 4 barrel carb & 4 barrel intake solve this?

A four barrel wouldn't be much help under about 3000 rpm, so if it is lazy off the line, that's not it.  Was it that way before you rebuilt it?  Maybe the front damper has slipped and your timing marks are wrong.  It's difficult to diagnose a problem from far away, we need some input from you so we can suggest solutions.

I’ll suggest checking out the distributor first.  Assuming the electrical part of the distributor is in good condition, then use a timing light to check out both the mechanical and vacuum advance portions.  With the timing light hooked up and reading the TDC mark on the damper, simply rev the engine up and observe the TDC mark with the vacuum advance line to the distributor both connected and disconnected.  You should see significant movement of the TDC mark in both instances but even more with the hose hooked up.  If you see no movement of the timing mark on the damper with the distributor hose unhooked when bringing up the rpms, then the distributor will need to be disassembled so that the mechanical advance portion of the distributor can be freed up.  If there is movement of the TDC mark when reving the engine with the hose unhooked but it doesn’t change when hooking up the hose, then the vacuum advance chamber or the hose itself is faulty.  If there is no movement of the TDC mark with the hose either hooked up or not while speeding up the engine, then both the mechanical and vacuum advance portions of the distributor need attention.

If the distributor checks out and isn’t the source of the problem, then other things to check and report on would include manifold vacuum readings and the results from doing a cranking compression test.

I know the timing is A1 perfect as is the distributor.

The car hums along nicely, I just have a flat spot on pull away, so I have to feather the throttle and pull away gently.

Once moving I can bowl along beautifully. Just the acceleration is gradual rather than rapid due to my flat spot.

See this video of a run we did on December 28th.

http://www.youtube.com/watch?v=mOICudPGjAw

About 15 seconds in you will see me pull away behind a red 55/56 Ford.

He shoots out, I move off slowly. The gold & white 59 Ranchero really pulls away fast & thats a Y.

As Paul mentions, a vacuum leak is a possibility and a vacuum gauge can help to determine this.

But assuming that checks out, is the accelerator pump pumping fuel when working the linkage?  Is the accelerator pump linkage adjusted correctly at the carb?  If there is free play in the accelerator pump arm in the idle position, then readjust the accelerator pump linkage so there is only 0.015” additional travel in the arm at full throttle.  Essentially, the pump diaphragm should be almost at the point of being bottomed out at full throttle when properly adjusted.

Turns out that I connected the vacuum pipe up wrong.

I had a dumb moment at some point & blanked off the vacuum pip from the intake manifold.

And then the pipe from the distributor, I connected to the carb overflow pipe!! Doh!!

So I had no vacuum advance for the distributor!

Theres always some clever clogs who remembers old pics!

Nice one.