by oli » Wed Aug 12, 2020 4:36 pm
Echo backpack power blower, PB-400E. Replaced carb with OEM Walbro, WA-55-1. Manual lists maximum high speed rpm of 7500 rpm. At 7500 rpm's measured with a reliable digital tachometer, the engine "4-cycles" and fluctuates from running smoothly to "4-cycling". Leaning out the hi-speed carb adjustment screw until the engine reached 8100 rpm's is when the "4-cycling" stopped and the engine smoothed out. Can I safely operate this machine at a higher rpm than indicated in the manual? Muffler, and exhaust port are clean. New air filter, fuel lines, and fuel filter. I allowed the engine to warm up before making adjustments. Machine was operated with the blower pipes. Thanks in advance.