I assume you are using muffler pressure to the fuel tank. Make certain that the muffler pressure connection at the muffler is open by inserting a needle into it and "feeling" for any stoppage. Do the same at the fuel tank. If there was a stoppage, re-adjust both the high and low speed valves/devises. If there was no stoppage, adjust the high and low valves/devices to be slightly richer. If there is still a problem, replace the plug.