Small Engines (Lawn Mowers, etc.): Tecumseh engine troubles, small engine mechanic, change spark plug

Question
I have a rider with a 12 hp tecumseh engine, sorry I don't have the details.  It didn't run the best, so I did as complete a tuneup as I could perform.  I did air filters, oil change, spark plug and rebuilt the carb, which I have done before.  The engine has good compression despite being about 15 years old.  Now it starts fine, but I can't get the carb dialled in just right.  It runs but not without the choke on, and no amount of tuning and tweaking will solve it.  I took the carb off and took it to a rebuild shop, had them rebuild it, and flow test it.  All is well with the carb, but still can't get the engine to run without the choke on.  Is there any known crankcase ventillation or vacuum issues with tecumseh?  Could it be a bad ignition module?  Wires?  I'm at my wit's end.  It runs fine, but not without the choke.

Answer
This is a classic fuel/air problem. Maybe you have a weak fuel pump. I would try replacing the fuel lines. There aren't any air leak problems I am familiar with, although I don't know it all. I would suggest you take the whole unit to an experienced small engine mechanic if none of these help.