Small Engines (Lawn Mowers, etc.): 8 hp briggs and stratton,riding lawn mower, briggs and stratton, internal passages

Question
I have a 80's homelite riding lawn mower.I changed the needle valve and the engine runs strong when idle,but when I engage the blade or drive forward or back, I lose all and power and the lawn mower will stall.Please let me know if you have any suggestions.Thanks

Answer
Make sure the mixture screw is adjusted to a starting point of 1 1/2 turns out from lightly seated.  If this makes no difference, open it another 1/2 turn and if there is still no change, the carb is dirty and will need to be cleaned thoroughly, including pushing a piece of tag wire through all of the internal passages and following up with aerosol carb cleaner.  Hope this helps.