How to Replace a Primer Bulb
Replacing primer bulbs in small engines is one of the most common types of tool repairs, and this article explains professional steps for primer bulb replacement in two engine design types.
The primer bulb has two hoses. Insert the primer bulb into it's housing for orientation to my explanation. The top hose of the bulb makes an immediate turn to the right; then passes back through a hole in a plate and attaches to the top of the carburetor (where the mixture screws are located). This is the hose that comes with the bulb kit. The bottom hose of the primer bulb is the return hose. It goes into the bottom of the gas tank. This hole is the one closest to the cutting head. Push it well into the tank. The third hose is the gas line hose. It connects to the filter inside the gas tank. It then passes out the other hole in the bottom of the gas tank. the hole that is closest to the carburetor. Insert the felt washer over the hose and push it up against the outside bottom of the tank. Now route this hose through s hole in the support plate and attach it to the bottom of the carburetor.
This would likely be due to failed reed valves inside the carburetor. Over time the valves will deteriorate away allowing fuel to flow freely through the carb and into the cylinder. Replacing the carb should solve the problem. The carb is part #753-1195.