Can you guess 21.2 CC two-stroke RPM?

I'm hoping somebody in here can guess what the RPM of a two-stroke 21.2 CC grass trimmer might be?
Out of curiosity... What's the displacement and RPM of a typical
gasoline engine RC aircraft?
FWIW. This is the grass trimmer owners manual, PDF document.
http://www.homedepot.com/catalog/pdfImages/d5/d568fa43-a88c-4a23-9bbd-8d0077b1ee26.pdf
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Thanks.

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John Doe wrote:

http://www.homedepot.com/catalog/pdfImages/d5/d568fa43-a88c-4a23-9bbd-8d0077b1ee26.pdf
Your best bet is to subscribe to RCGroups.com, and ask these questions there.
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HPT
George Hostler
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On Mon, 15 Oct 2012 04:42:50 +0000 (UTC), John Doe

I have had a 17cc B&D strimmer for years could easily take a tacho reading if that would help? NB speeds up quite a bit when the cutting nylons get worn down short so ther is a bracket of RPM. C+
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Charlie+ <charlie xxx.net> wrote:

If it's two-stroke, and no trouble, Yes, thanks.

I'm concerned about maximum RPM.
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On Wed, 17 Oct 2012 20:23:06 +0000 (UTC), John Doe

Ok Here you go... Max rpm with full length nylons = 6701 Max rpm with worn down nylons to 2" = 7524 At the 7524 figure the engine is beginning to miss slightly so for full power strokes use the 6701 figure. There is no gearing so this is the engine rpm. Accuracy +1/-1 rpm. The engine is properly tuned. C+
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