Brush cutter funny noise.

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Jan 20, 2021
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Hi. I have a Stihl Fs450 brush cutter I'm busy repairing. I did a full service on it and also replaced a few parts that was damaged. When I was busy fine tuning it at a certain point it makes a hollow sound when I open the throttle before picking up revs. What can be the cause? And also when running at full throttle it almost sound like it is over revving but according to the Rev count its still below its normal operating revs.
 

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Lawn Royalty
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First the unit is rev limited to 12,500 rpm so you may hitting the rev limiter. Max rpm needs to adjusted to be just below the max rpm limit by enriching the fuel mixture if necessary.

As for hollow sound it may be the clutch sticking or worn out clutch drum. Just a thought as I am not there to hear the sound myself.
 
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The revs is only at 9000 rpm's wen its sounds like it's over revving.
 
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