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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Ignition Timing Related Posts
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<blockquote data-quote="Magnetoman" data-source="post: 107216" data-attributes="member: 2806"><p>Personally, I always follow the double tap rule.</p><p></p><p> [MEDIA=youtube]JmA2WYyw-_A[/MEDIA]</p><p></p><p>However, the details get complicated. I use the inductance of the primary to determine when the points open, since that changes from 0.00 (on the mH scale) to ~5 so there's no mistaking it. However, when you have a resolution of ~0.1-deg. the inductance doesn't just abruptly jump between those two limits. It sort of oozes between them. Further, if I stop advancing the engine just before the full value is reached (or anywhere up to that point) and wait, it slowly oozes lower over a period of many seconds. I think part of that oozing may be due to backlash of the gears relaxing, but some of it may be due to the points rubbing block relaxing under the pressure of being held partially open by the spring. If I had ~10x lower resolution, so I could tell the difference between 38-deg. and 39-deg., but no better than that, I wouldn't see these effects.</p><p></p><p>If I'm right about the relaxation issues, both would be different in operation. The engine would keep pressure on the gear train so there wouldn't be an opportunity for the backlash to relax, and the rubbing block would take on some steady-state amount of relaxation. The only way to know how much an effect this would have would be to accurately set the static timing, then check the timing with the engine running.</p><p></p><p>The other "detail" is the value of advance to use. Fifty years ago my Gold Star was tested by the factory at "39 degrees." I can set it to 39.0+/-0.1 degrees but with today's fuels, would it be better to use something other than 39 degrees? Unfortunately, I haven't found any definitive information on this. Yes, there are plenty of unsubstantiated allegations that more/less advance is needed because modern fuels burn slower/faster, but I've yet to find any actual data showing one or the other. </p><p></p><p>[ATTACH=full]27018[/ATTACH]</p></blockquote><p></p>
[QUOTE="Magnetoman, post: 107216, member: 2806"] Personally, I always follow the double tap rule. [MEDIA=youtube]JmA2WYyw-_A[/MEDIA] However, the details get complicated. I use the inductance of the primary to determine when the points open, since that changes from 0.00 (on the mH scale) to ~5 so there's no mistaking it. However, when you have a resolution of ~0.1-deg. the inductance doesn't just abruptly jump between those two limits. It sort of oozes between them. Further, if I stop advancing the engine just before the full value is reached (or anywhere up to that point) and wait, it slowly oozes lower over a period of many seconds. I think part of that oozing may be due to backlash of the gears relaxing, but some of it may be due to the points rubbing block relaxing under the pressure of being held partially open by the spring. If I had ~10x lower resolution, so I could tell the difference between 38-deg. and 39-deg., but no better than that, I wouldn't see these effects. If I'm right about the relaxation issues, both would be different in operation. The engine would keep pressure on the gear train so there wouldn't be an opportunity for the backlash to relax, and the rubbing block would take on some steady-state amount of relaxation. The only way to know how much an effect this would have would be to accurately set the static timing, then check the timing with the engine running. The other "detail" is the value of advance to use. Fifty years ago my Gold Star was tested by the factory at "39 degrees." I can set it to 39.0+/-0.1 degrees but with today's fuels, would it be better to use something other than 39 degrees? Unfortunately, I haven't found any definitive information on this. Yes, there are plenty of unsubstantiated allegations that more/less advance is needed because modern fuels burn slower/faster, but I've yet to find any actual data showing one or the other. [ATTACH type="full" alt="27018"]27018[/ATTACH] [/QUOTE]
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