Lionel 773 1950 Smoke Lever Operation Question

There is a tang on the left hand crosshead that pushes the smoke lever with the arm down. The smoke lever the pushes the  piston inside the cylinder of the smoke unit. So most likely the tang on the crosshead is bent or missing or the piston cup is stuck in the cylinder or missing. Another source of the problem is a blocked air port in the pellet cup from too many pellets. The tang on the crosshead is to move the smoke lever forward, not back, that  happens with gravity.

Everything @Chuck Sartor rings true. Additionally, you can ad a 2026-44 spring between the top of the piston and the cup can help with the return.

You need the service manual for the 773. It illustrates the locomotive fairly well.  It has been published in a number of the service manual reprints.

Another potential issue with 773 smoke is that there is a recess cast into the steam chest for the smoke lever.  Many of the smoke levers were not well formed and do not interface with the steam chest well.  This results in the smoke lever having very short travel, which produces very little smoke piston travel.   A proper smoke lever was sold for many years, but I have not seen one recently.

Thanks to all who replied. Last night I took another look at the 773 and the tang on the left-hand crosshead is there; I'd seen it the first time I looked at it but it was ahead (meaning forward) of the smoke lever, so the as it moved back and forth the smoke lever was just hanging straight down doing nothing. The tang also looked like it had slid forward 1/8 - 3/16" or so on the crosshead shaft (or piston rod on a real locomotive). As I operated the smoke lever manually back and forth with a small screwdriver, when it was as far forward as it would go, it looked like if the tang was behind the lever, it would jam the crosshead not allowing it to travel far enough forward. This was confirmed last night; as I took a closer look at it, it now looked as though the tang was far enough back on the crosshead shaft to fit behind the smoke lever. I tried fitting the crosshead with the tang located behind the smoke lever, operating it by hand before I reconnected the main drive rod to the center drive wheel. It seemed to operate okay, so I reassembled the rods and tried it on the track under power. The loco only moved a short distance forward before the left-hand side rods jammed to the point that the piston shaft with the tang on it was pulled completely out of the crosshead. I disassembled the crosshead and gently tapped the shaft back into place, but something is still definitely wrong. I feel that I'm on the right track now, but now I'm wondering if the smoke lever needs to be "adjusted" (meaning carefully bent forward to allow it to travel farther forward), or maybe there's something limiting the upward travel of the smoke unit piston. I'm going to have to remove the boiler shell from the frame and take a look at the smoke unit itself to check for anything that might be amiss.

Check that the smoke unit mounting screw is not too long and the piston is hanging up on the screw.

Thanks - I'll definitely check that

Problem Solved! I took the boiler shell off and everything looked okay with the smoke unit, so I gently "adjusted" (bent) the smoke lever to allow it to travel farther forward, and now the 773 is puffing away happily as intended. Thanks to all for your input and advice!

Great Tom….how about a video of this happy puffer….