I'm no expert but sounds like when I had a pinched fuel line which makes me think you have a partially clogged carb. Maybe some fuel treatment run though it could clear it. Empty your tank and run a little bit of seafoam or comparable additive at higher percentage then normal and it might just run through and clear it.
You could also make sure your air filter is clean and you don't have any gasket leaks. And then there's your spark plug. Check color of burn and gap...test for spark. Could be that it's not burning hot enough.