Re: lta-50, runs terrible
Clean the air filter, pull the carb apart and clean the bowl and jets, and pull the spark plug. Mine used to get a little piece of carbon stuck in the elctrode, causing the exact problem you described.
Those little motors carbon up really easy, you may want to pull the exhaust off and make sure it's not clogged. I also switched to Motul 600 oil after being told it leaves almost no carbon behind.
When pulling the carb, look and see if the intake elbow restrictor is still in there.