I have a Sears string trimmer 358.799260 with a Walbro carb. At first when I pressed the bulb before starting, it would not return. Now it returns, but will not pull gas through the carb. The fuel filter is fine; the valves in the bulb are fine; the diaphram seems okay. Any suggestions? E4 WT298 N7 5-5477 The bulb is remote by one inch.