Small Engines (Lawn Mowers, etc.): Poulan PO1742STC riding mower, google, gas cap

Question
After I cut my lawn for the last time last summer, I forgot to drain the oil. So, the mower sat for the winter. I have taken it out for the season again, drained and refilled the oil. When I start the mower, it runs. But if it could actually "cough", that's the sound it would be making, because it sounds like it's coughing and choking. And black smoke coming from the exhaust. I have let it sit and run and run until the gas ran out and no change. I changed the spark plug also. Lastly, when I put it into gear, it rides, but it only rides as if it's still in first gear. It seems as if it wants to shut off also, and a couple of times it did just that. I typed "Poulan PO1742STC" into Google and found a detailed repair parts schematic manual. Where do you suggest I start? Thank you so much, in advance for any advice you can give to me. I am a do it yourself kind o gal when I can be, but if I need to have someone else look at this, then so be it...:(

Answer
Hi Theresa,

I would try adjusting the carb.  The high speed mixture screw is initially set at 1&1/2 turns out.  Then adjust it to give good acceleration and top speed while keeping the screw as far out as possible.  The low speed mixture screw is set at 3/4 turn out, then adjust to give a smooth idle.   If no change, then the carb most likely has dirt, debris or gummed fuel inside.
First, check the gas cap to make sure it is venting and not causing a vacuum in the tank.  If that's okay, you will need to remove the carb, disassemble it, clean all the small internal openings and blow it out with compressed air.   Probe each and every hole with a small wire.   A carb rebuild kit wouldn't hurt either.  

Let me know how you make out.
Michael