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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Ignition Advance
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<blockquote data-quote="Martyn Goodwin" data-source="post: 128536" data-attributes="member: 2433"><p>Hi Greg,</p><p></p><p>After my last piston replacement and the fitting of th decomp plate I checked out the action of my ATD and found as you suggested that the springs in it were rather weak. I also took a look at the ATD curves available on the brightspark web site that show the impact of weak springs on the rate of advance - the two lines of interest are the Pink - far left - where there are NO SPRINGS and the Orange on the right with two preloaded springs</p><p></p><p>[ATTACH=full]37799[/ATTACH]</p><p></p><p>I obtained a set of new ATD springs and in the hope of flattening the advance curve - that is needing more revs to get it to move to full advance, I modified the 'bob' weights, reducing their mass. this means (in theory) the need for higher revs before full advance is reached.</p><p></p><p>In this photo the original 'bob' weight is on the left and my lightened version on the right.</p><p></p><p>[ATTACH=full]37798[/ATTACH]</p><p></p><p>So far I , as a result on newly imposed covid restrictions, I have not been able to road test the impact of the change to the 'bob' weights but with the inspection cover removed I have visually confirmed that the magneto still functions correctly, moving to full advance, as I increase revs with the bike on its stand. </p><p></p><p>With the weights lighter, basic physics dictate that the advance must be reached at higher revs than before. </p><p></p><p>I am trying to locate a calibrated strobe light/tacho so I can measure the RPM at the point of advance commencing and also at the point where full advance is reached - any ideas?</p><p></p><p>Martyn</p></blockquote><p></p>
[QUOTE="Martyn Goodwin, post: 128536, member: 2433"] Hi Greg, After my last piston replacement and the fitting of th decomp plate I checked out the action of my ATD and found as you suggested that the springs in it were rather weak. I also took a look at the ATD curves available on the brightspark web site that show the impact of weak springs on the rate of advance - the two lines of interest are the Pink - far left - where there are NO SPRINGS and the Orange on the right with two preloaded springs [ATTACH type="full"]37799[/ATTACH] I obtained a set of new ATD springs and in the hope of flattening the advance curve - that is needing more revs to get it to move to full advance, I modified the 'bob' weights, reducing their mass. this means (in theory) the need for higher revs before full advance is reached. In this photo the original 'bob' weight is on the left and my lightened version on the right. [ATTACH type="full"]37798[/ATTACH] So far I , as a result on newly imposed covid restrictions, I have not been able to road test the impact of the change to the 'bob' weights but with the inspection cover removed I have visually confirmed that the magneto still functions correctly, moving to full advance, as I increase revs with the bike on its stand. With the weights lighter, basic physics dictate that the advance must be reached at higher revs than before. I am trying to locate a calibrated strobe light/tacho so I can measure the RPM at the point of advance commencing and also at the point where full advance is reached - any ideas? Martyn [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Ignition Advance
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