WHEN I START IT,IT RUNS ONLY THE AMOUNT OF PRIMED ...

Check the fuel filter, air cleaner, and muffler for plugging. Check the condition of the fuel lines for rot, hardness or splitting. Check the carburetor fasteners for tightness. If still no help, remove the carburetor from the engine and check the crankcase impulse passage from the cylinder, through the gaskets and heat isolator block. Inspect the piston skirt and cylinder wall for any serious scoring or other damage while the carburetor is off. Remove the upper chamber cover and inspect the valving and small diaphragm for any cracking or other damage. This chamber uses crankcase pressure impulses to cause the fuel to be pumped from the tank. Hope this helps!