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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modern Fuel & Ignition Advance
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<blockquote data-quote="Pete Appleton" data-source="post: 94944" data-attributes="member: 145"><p>David mentions 'doing what the factory did' That would indeed be an interesting exercise to repeat with modern fuels and would go a long way towards answering the question posed by the original post.</p><p>I suspect that the factory were working around the problems of using mechanical advance systems. Perhaps they just picked a final advance figure that gave the best compromise at all rev ranges. </p><p>Today I set up a series 'D' distributor on my electronic ignition test rig ( alright, it is an old food blender and an oscilloscope) the purple line on the graph below is what I found. In fact the curve is so different from what I expected that I did it all again to check my measurements. </p><p>The three plots are very different. At some rev ranges there is a difference of 10 degrees. Assuming that the published figures for bth and pazon are accurate then someone ( or everyone) must have it wrong. My interpretation of the information provided by Grey One makes me think that the advance curve should ideally flatten out at the top end, or even head back down again. That would all be very difficult to do mechanically. </p><p>I also tried to do the graph for a magneto with ATD. Unfortunately that wouldn't go on my state of the art analyser so I had a go at doing it on the lathe. The maximum speed achievable with that was 2000 crank rpm but there was almost no detectable advance movement at those speeds. I will have to build a better mag test rig. Has anyone done the degree wheel/strobe test with a mag?</p><p>As per OldHaven I have been working with programmable ignition systems. They are very successful but what curve do you program?</p><p>Of course we could find that it makes very little difference and we should just set it to 36 degrees and get on with riding it.</p><p>[ATTACH=full]21992[/ATTACH]</p></blockquote><p></p>
[QUOTE="Pete Appleton, post: 94944, member: 145"] David mentions 'doing what the factory did' That would indeed be an interesting exercise to repeat with modern fuels and would go a long way towards answering the question posed by the original post. I suspect that the factory were working around the problems of using mechanical advance systems. Perhaps they just picked a final advance figure that gave the best compromise at all rev ranges. Today I set up a series 'D' distributor on my electronic ignition test rig ( alright, it is an old food blender and an oscilloscope) the purple line on the graph below is what I found. In fact the curve is so different from what I expected that I did it all again to check my measurements. The three plots are very different. At some rev ranges there is a difference of 10 degrees. Assuming that the published figures for bth and pazon are accurate then someone ( or everyone) must have it wrong. My interpretation of the information provided by Grey One makes me think that the advance curve should ideally flatten out at the top end, or even head back down again. That would all be very difficult to do mechanically. I also tried to do the graph for a magneto with ATD. Unfortunately that wouldn't go on my state of the art analyser so I had a go at doing it on the lathe. The maximum speed achievable with that was 2000 crank rpm but there was almost no detectable advance movement at those speeds. I will have to build a better mag test rig. Has anyone done the degree wheel/strobe test with a mag? As per OldHaven I have been working with programmable ignition systems. They are very successful but what curve do you program? Of course we could find that it makes very little difference and we should just set it to 36 degrees and get on with riding it. [ATTACH=full]21992[/ATTACH] [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modern Fuel & Ignition Advance
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