I will look it up, but I think some Walbro carbs have a primer that works like this....there is a well (chamber) that holds fuel with a mesh screen over it. When the throttle is opened it puts draw on this well and the fuel in it richens up the mixture on acceleration. The screen kinda regulates the am out of fuel so there is not too much all drawn in allat once. This is by memory...could be wrong...I was wrong at least once...butI cannot remember. Read that too! Capt,n