We'll need a little more information to offer any help. What engine? What carburetor?
2 stroke or 4?
Always provide details when asking for advice. It makes it much easier for us to offer accurate information.
Take a look at the slide to make sure it is free to go up and down, if it is good you might just have an airleak at the carb to manifold joint. Make sure the carb is pressed firmly onto the manifold and tighten the clamp while pressing it there.
They leak there quite a bit.
Hope this helps!