Echo PB400E High Speed Adjustment

[oli]

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.

[KE4AVB]

It should be fine; although, I think you may have a little less restrictive in discharge causing less of a load on the blower fan. Service info that I have indicates using three sections of tubes when setting the rpm. One model in that series does run at 8000 rpms.