Classic/Antique Car Repair: backfire, old timer, compression test

Question
My 1929 Model A lost water, started to backfire and wouldn't run.  After we took the head off, We found a cracked valve.  Replaced all valves, springs and guides. Sent head to machine shop. Installed leakless water pump.  Engine now idles ok but is rough under load and backfires.  Can't drive as it has no power. Changed condenser, timed, did compression test, rebuilt carb, etc.  AM wondering if this could be a case where one or two of the rings have failed and I need to install new rings.  Or if their are other problems.  I don't want a new engine unless there is no choice. My mechanic owns his own Model A and is no stranger to this but can't get it to run.

Answer
The only thing that comes to mind are the points, but I'm sure you checked those out.  If it has good compression, is timed properly, clean plugs, gas, good carb., idles good, ????? That's a tough one.  I recently ran into a car where the point arm spring broke and there was very little force against the cam.  The point arm would float above idle.  Pull it back with your finger and make sure it is not weak or broken.  If that does not do it, then put new points in. I don't think the coil is the prob.  There is a higher probability that a new condenser is bad, than a good condenser going bad.  I put in a new one once, then tried to fix everything else, until an old timer flipped the points and said the cond. was bad.  The A can cook the cond. from the manifold heat, but not very often. Try it with new points and the old condenser, after you know that the arm spring is good.  Let me know what you find out.  jack

I thought of two more things you might check.  If you put on a new gas line, make sure you did not place the ferrule too far from the end going into the carb.  If the tube extends too far into the carb, it will hit the screen and block flow into the bowl.  It will idle, but there will not be enough gas under load.
The other thing is to open up your mixture at the choke rod and see if that clears things up.  If it does, then you need to take another look at the carb.  jack