Look at the accelerator pump first. Take off the air cleaner and using a flash light watch the squirter while you open the throttle. You should see a stream of fuel immediately into both venturies. Adjust the pump arm if you aren't getting that shot just as the throttle opens. In my case I had to increase the jet size to fix a bog but if the carb was rebuilt with all the same settings it's probably just an adjustment somewhere. Check to make sure all the nuts (carb to manifold) are still tight since you just installed it recently.