Ignition Timing Chart for Puch

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Here is a handy chart for converting Puch ignition timing from degrees before top dead center to millimeters before top dead center and vice versa.

http://www.mopedarmy.com/forums/file.php/7/84148/puch_timing_sheet_5in_wheel.pdf

Puch timing chart.jpg


1469940815523.png

This can be calculated from basic trigonometry.

L = conrod length (in mm) - usually it's a little more than twice the stroke. Puch is ~90mm

a = crank effective radius, which is 1/2 the stroke. for puch, stroke = 43mm, a=21.5

then a*cosΘ plus the square root of ( L^2 + (a*sin Θ)^2) gives you the height h (shown in pic)

and if conrod length (L) plus crank radius (a) is height (h) at TDC, just subtract that value from your calculated h, and you have mm BTDC

[(a*cosΘ) + sqrt( L^2 + (a*sin Θ)^2)] - (L+a) = mm BTDC for given degree Θ

  • make sure you're consistent using radians or degrees, or if needed convert degrees to radians:

radians = (degrees / 180)*pi