To fix a Walbro carburetor, first identify the main problem, such as the filter clogging, the internal needle valve leaking or the pop-off pressure being out of normal range. The pump may also run lean or be hard to start.
If the small filter at the fuel intake is clogged, remove it, and spray carburetor cleaner through it in the direction opposite to the fuel flow direction. Afterwards, reinsert it using a pencil eraser.
If the internal needle valve is leaking, it's old or worn out. To rectify the problem, replace the needle valve, and adjust it to the same level as the carburetor housing. If you don't have a gauge, position it slightly lower than the carburetor housing.
If the pump is hard to start or running lean, the fuel pump membrane is stretched or hardened. To fix the problem and prevent future occurrences, occasionally replace the membrane. If the pop-off pressure is out of normal range, the spring is cut, overstretched or incompatible with the carburetor. Replace the spring to resolve the problem.
In case of an erratic idle or no idle at all, inspect the internal needle valve and the float diaphragm for signs of damage. Additionally, look for air leaks.