At full throttle the unit will not run full speed. It sounds like it has exhaust ports clogged. I ensured that the spark arrestor is out, the ports are cleaned. I put a new filter, vent, spart plug, gas filter, gas lines and a new seal on the starter rope side of the crank. I took the carb apart and cleaned and then I took carb off another echo and put it on this unit with no luck. I don't see any leaks at head gasket. The last thing is ignition coil0 is it reasonable that it could cause this kind of problem. The unit is 2 years old with very low use...gas was changed out twice.