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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Still Can't Start My Twin, Replaced Mag, But Not A Pop
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<blockquote data-quote="DucATIRadeon" data-source="post: 174127" data-attributes="member: 5456"><p>hope not to kick against any sore shins, try the ignition form another approach (perhaps even simpler?):</p><p>- set the nr 1 cylinder at TDC as per usual</p><p>- retard the crank only 8 degrees (ccw).</p><p>- set the mag with the points at the correct lobe, just at the cracking point (light on/off).</p><p>- mount the ATD on the mag without disturbing the mag. DO NOT advance the ATD fully, leave it at rest or fully home in the most retarded position.</p><p></p><p>at least now you know that the static ignition is at 8 degrees BTDC, and not even retarded few degrees ATDC.</p><p>I did this to my rapide after fidgeting at 38degrees BTDC and ATD full advance etc., and it works pretty well! the old ATD will have indents to where the advancing arms hammer into the other arms. this affects both variable timing range and starting point.</p><p>why: the Enfield has identical bore and stroke and even similar compression ratio and valve sizes, so a very good comparison. there it is set at 8 degrees BTDC, works a treat.</p><p></p><p>going into detail (its pretty much geometry):</p><p>measure the diameter across the ATD where the advancer has indented its max stops. divide by 2 to get a radius figure.</p><p>then measure the gap between the advancer and the stops (this is the range in which the ATD can vary its timing).</p><p>you have 2 radii and a gap, and the triangle it forms has a small included angle. calculate that angle (here comes the geometry into play) (will be in the range of 10-15 degrees).</p><p>multiply that angle by 2 will give you the timing range of that ATD. let call that angle beta.</p><p></p><p>therefore: setting max advance at 35degrees BTDC will give you a (35 - beta)degrees static at low idle. for example, beta = 26degrees. the static will be 35-26 = 9degrees (the larger the static advance the higher the chance of getting kick-back).</p><p>setting the ignition form static approach: 8 degrees BTDC + beta = 8 + 26 = 34 degrees.</p><p>should you have a new ATD without indented arms the range is less than a worn example. therefore, if timing set at max advance, the static can be more and give you a potential kick-back.</p><p></p><p>anyway, just an idea.</p><p>my ATD is worn a bit and set at 8degrees BTDC static, giving a max advance of 38degrees.</p><p>what I do do is tie a thread from the ATD to a heavier object so all the slack in the drivetrain is removed when setting the timing.</p><p>note: picture inserted is showing my ATD at max advance and slack out of the drivetrain, when setting at 38degrees BTDC.</p></blockquote><p></p>
[QUOTE="DucATIRadeon, post: 174127, member: 5456"] hope not to kick against any sore shins, try the ignition form another approach (perhaps even simpler?): - set the nr 1 cylinder at TDC as per usual - retard the crank only 8 degrees (ccw). - set the mag with the points at the correct lobe, just at the cracking point (light on/off). - mount the ATD on the mag without disturbing the mag. DO NOT advance the ATD fully, leave it at rest or fully home in the most retarded position. at least now you know that the static ignition is at 8 degrees BTDC, and not even retarded few degrees ATDC. I did this to my rapide after fidgeting at 38degrees BTDC and ATD full advance etc., and it works pretty well! the old ATD will have indents to where the advancing arms hammer into the other arms. this affects both variable timing range and starting point. why: the Enfield has identical bore and stroke and even similar compression ratio and valve sizes, so a very good comparison. there it is set at 8 degrees BTDC, works a treat. going into detail (its pretty much geometry): measure the diameter across the ATD where the advancer has indented its max stops. divide by 2 to get a radius figure. then measure the gap between the advancer and the stops (this is the range in which the ATD can vary its timing). you have 2 radii and a gap, and the triangle it forms has a small included angle. calculate that angle (here comes the geometry into play) (will be in the range of 10-15 degrees). multiply that angle by 2 will give you the timing range of that ATD. let call that angle beta. therefore: setting max advance at 35degrees BTDC will give you a (35 - beta)degrees static at low idle. for example, beta = 26degrees. the static will be 35-26 = 9degrees (the larger the static advance the higher the chance of getting kick-back). setting the ignition form static approach: 8 degrees BTDC + beta = 8 + 26 = 34 degrees. should you have a new ATD without indented arms the range is less than a worn example. therefore, if timing set at max advance, the static can be more and give you a potential kick-back. anyway, just an idea. my ATD is worn a bit and set at 8degrees BTDC static, giving a max advance of 38degrees. what I do do is tie a thread from the ATD to a heavier object so all the slack in the drivetrain is removed when setting the timing. note: picture inserted is showing my ATD at max advance and slack out of the drivetrain, when setting at 38degrees BTDC. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Still Can't Start My Twin, Replaced Mag, But Not A Pop
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