I would avoid that repair shop in the future, go find one with a tech thats knows something about walbros...

Scota4570
Those carbs are designed to work with engines using the stratified charge principal. The stratified charge principal is a way of reducing unburned hydrocarbons from exiting engine. During the end of the exhaust phase and prior to the transfer phase, plain air is let into the engine the create a wedge of air with no fuel into cylinder to go between exhaust gas and incoming air fuel mixture coming from transfer ports a few degrees later, so it dosen't go out the exhaust port.

Redmax uses this approach and its explained on their website.

You could block off top hole.I personaly would find another engine.