Disconnect the fuel line at the carb and see if you get a good tream of fuel when the tap is opened. The filter in the tank might be plugged. It might be starving for fuel. That is why when it bogs you are getting too much air in relation to the amount of fuel thqat i flowing and when you close the throttle you choke back the air and bring the fuel/air ratio back into balance.
It is also possible that your fuel tank vent is plugged. When it bogs try opening the cap to see if it clears up.