I have a 1954 Mercury with a 256 with a factory 4bbl teapot carb that has been rebuilt by Carb Junkys. My problem started before the rebuild. It starts easy and idles great, and I can rev it about 1000 rpms before it boggs down and begins to backfire thru the carb. It has even caught fire and was able to put it out with a rag. I have changed the condensor, points, rotor and reset the timing. Plugs and wires are new last fall. I have played with the timing but nothing helps. Any suggestions? I have also developed a large hole in the muffler. Could that be the problem?
Thanks, Gary

Have you performed a fuel pressure / volume check of the fuel pump?  This is not high on my list if the problem simply shows up when free revving the engine but is worth eliminating just the same. 
 
Assuming the ground strap within the distributor is in good shape, I’ll suggest replacing the coil.  Also check that the ground strap from the firewall to the engine is intact.

Lorena, Texas (South of Waco)

It might be a case of sticky valves, or the float set too high in the carb letting it run too lean.

Try checking the vacuume pot on the distributor is working also.


  AussieBill            YYYY    Forever Y Block     YYYY

 Down Under, Australia

1st I know absolutely nothing re tea pots (4000 carbs ?)
You say it back fired thro the carb, I had that happen with a 4100 and I think I've wrecked the power valve. Does a tea pot have a power valve?
It may not be your initial problem but it is something to consider.
Feel free to shoot me down I can take it.
stuey

Stuey.  This is not meant to shoot you down but simply provide some info on the Teapot carbs.
 
The 1953 & 1954 Holley 4V carbs are actually a model 2140 carb which is the predecessor to the Holley model 4000 carbs.  The power valves in the 2140 and 4000 carbs are pretty much impervious to damage from a backfire being brass in construction and reusable for the life of the carb if driven regularly.  The power valve actuators on the other hand are problematic in sealing at the fuel bowl cover and while backfiring should not present a problem even for those, I can see where a backfire might break the actuator cover seal assuming it’s making a decent seal to begin with.  The enrichment circuit is reasonably small though so even with the power valve being actuated all the time, the only detriment to that would be a drop in the fuel mileage while drivability in itself is basically unaffected.
 
Bill’s suggestion regarding the vacuum to the distributor is a good one.  Checking the timing with a light while running the engine rpms up and down would help to verify if the distributor ignition curve is functioning as it should or not.

Lorena, Texas (South of Waco)

Listen to the advice from Ted Eaton. I was going to post the same info, but he beat me too it. I agree about being difficult to blow out a power valve economizer (actuator) in a 2140 or 4000 Holley teapot, since the rubber diaphragm part is backed by metal and can't expand far enough to blow out with a back fire.
  Sal

Thanks for the heads up folks.
More nuggets of info, I greatly appreciate it.
stuey