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rick- Engines need three things to run properly: 1) Good spark (whitiesh/blue color) delivered to each cylinder at the proper time. 2) Good fuel/air mixture delivered to each cylinder in proper quatitity. 3) Sufficient compression.
Poor performance/dies/sputters under laod is most often SPARK related.
Now, as to spark , I have to assume your tune-up procedures and (I don;t mean any insult) mechanical abilities are correct and thorough. I.e., your point gap is right on target, connections are all clean/bright/tight, plug wires are incorrect firing order and are of copper core type (not off-th-shelf automotive type). If so, you can take an old,properly gapped plug and ground it to the engine block, crank engine and see that REQUIRED whtiesh/blue spark and KNOW at least that spark is good. If it isn't you must track it down before doing anything else. Otherwise, you may chase a lotta ghosts.
Assuming spak is good AND plug wires in proper order AND base timing is set correctly, then if you've run down the normal list of fuel related things (fuel screens, carb settings, float settings, etc.), then check your manifold for leaks. A leaking intake gasket will lean out your fuel mixture and cause sputtering/dying. If that's okay, check valve lash. An improper lash will not allow sufficient fuel/air mix into the cylinders (it will close to early so not enough mix gets in). If all above checks out, then perform a dry then wet compression check. Don't haapen to know the minimum comp #s, but they are available in the specs to the left. Poor compression can becaused by worn rings, worn sleeves, rings not installed properly, burned/bent/improprely lashed valves, carbon,obstructions, head gasket leak - several things. Hope that gives you some more ideas.
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