2-Stroke spark knock?

[bharen]

What does 'spark knock' (pinging) sound like on a 2-stroke engine? On both my chainsaw and new brushcutter (both Stihl) I regularly hear what I'd call a metallic 'rattle' when I blip the throttle. The noise seems to go away when I open both engines up to full throttle. I'm running 89 octane gas at the recommended 50:1 mix. Thanks in advance!

 

[bwalker]

What you are hearing is the motor misfiring. Two strokes routinely do this at low rpm. A two cycle spark knock usually occurs around 3/4 throttle under heavy load. The engine feals like it is low on power when it happens and the sound itself has a rapid high pitched ring to it.

 

[Tony Snyder]

It is also possible that you may be hearing the rattle of incomplete clutch shoe engagement that occures either at idle or just before enough rpm has been gained to establish solid clutch shoe engagement.

Either what Ben suggest or what I suggest are possibilities, but they would sound very different.

 

[bharen]

Thanks!

Thanks for the replies, gents. Much appreciated. Puts my (often feeble) mind at ease.

 

[bwalker]

One more thing. Stihl all my stihl trimmers (fs85,200,250) make a mettalic noise when the clutch engages or diengages.

 

[ChiefJack]

I have a Stihl 240 brush cutter that is doing the same thing. Sounds like a pinging noise in low idle. Will I damage my brush cutter if I keep running it the way it is? Should this seek immediate attention? Can I fix it myself?