I can't get my Troy-Bilt Blower TB320BV to Prime

When priming a carburetor, the vacuum created by the bulb is pulling the fuel through a long circuit that includes subsystems which wear and begin to leak over time.

In some cases, it can be as simple as a fuel line that has begun to crack or has completely broken. In these cases, the engine may prime and run normally when the fuel tank is completely topped, but it will begin to run or prime erratically once the level drops.

In others, it may be a leaking main jet, low speed check valve, or an accelerator pump (pumps are usually found on higher end equipment). These three are generally not repairable without special pressure/vacuum testing, proprietary tools, unusual parts, and retesting.

This is why most shops will not even offer lengthy carburetor rebuilds when a new one is usually $50 or less. These three issues can also cause a lean condition that will eventually destroy the piston and cylinder, so it is not recommended to operate any engine with these problems.

Many higher end Zama carburetors in production today don't offer a low speed check valve from the dealer, so this type of failure is not repairable and the carburetor can only be replaced.

The two check valves in the carburetor's primer flange (or remote fuel bulb assembly) must also function properly for the entire fuel system to work properly. The function of these two can be seen on cheap brands that use clear fuel lines. Make sure the bubbles are traveling in one direction with no reversal as the bulb is released.

If the primer flange or remote pump assembly is all that is failing, the unit can still be operated with no fear of lean issues that can cause expensive damage. Expect to pull that starter rope several more times to get the unit running.

I recommend inspecting the cylinder and piston to be sure there is no scoring or visible damage before attempting to diagnose or repair anything. Carefully remove the muffler, rotate the crank, and use a small flashlight to inspect all of the internal surfaces. If all is well and the fuel lines are in good shape, swap the carburetor and fuel pickup (filter) for new ones. This is usually feasible for units that aren't plagued with other issues.