Sounds like fuel starvation.
Check rate of fuel flow from tank to carb. Pull fuel line at the carb and drain fuel into a clear transparent container. Watch to see that fuel is flowing freely. If it isn't, you have a restriction in the fuel tank or fuel line. Let the fuel settle in the container and take a good look for dirt or water in the fuel. If it has either, drain all fuel from the tank and thoroughly wash it out. Sounds like a crappy job and it is. However, you got to do what you got to do. If the fuel is clean, pull your carb and remove the fuel bowl. Take it off nice and easy and look for contamination in there as well. If it's dirty, a complete carb cleaning will be required. That means removing and cleaning all jets and passages then blowing out same with compressed air. If there is no fuel in the float bowl, that would lead me to suspect that the float valve needle is probably stuck in the seat. Carefully remove the float needle and clean it and the needle seat as well. Use a very thin piece of single strand copper wire to clear small passages then blow them out was best you can.
While you're at it, clean your air filter and change your oil if you haven't done so already. Check your spark plug(s) and inspect their condition also. See if they are dry or wet with fuel. If they're dry, that will indicate a fuel starvation problem. If they're wet then it's a flooding problem. If wet (probably not) make sure your choke is working properly.
Good luck.
