When you get the prop installed and question your placement of the sensor here is a method to quickly check just how many degrees you have it set BTDC.

To find straight line distance between points on arc:
Q&D : {Circumference=(diameter x pi)} * {degrees of arc = timing degrees} / 360
Dia: 1.372" 4.310
Tim Degree: 25

Straight line dist: 0.2993"

Formal calc method:

2r * sin (1/2 degrees)
2r=dia 1.372"
sin (25/2) 0.2182

S line dist: 0.2993"

Close enough for dial calipers!

Just installed a CH Ign on a Ryobi and with good spark (plug out), carb and plug damp with fuel, and just get one mild POP and then nothing. Above method should allow measurement, without removing prop and tinkering with a timing wheel.

This alternate method should allow a quick check of timing anytime you desire.

How many degrees do Ryobi like for an initial BTDC setting? The supplied instructions stated to 'align to the mark on the sensor hose clamp' The mark was rather wide.

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