If it idles and wont rev up you need to check a few things.

Make sure the fuel line has no leaks and the primer bulb is pumping up hard.

Make sure the fuel tank is vented.

Check/replace the fuel pump diaphram.

If the motor sat a long time you could need to have the carbs rebuilt... idling
with no power is usually a sign the carbs are gummed up and will have to be
rebuilt.

The seal is fairly easy if you know what your doing... get a service manual.