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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Comet Ignition Timing 2018
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<blockquote data-quote="oexing" data-source="post: 97094" data-attributes="member: 1493"><p>Nothing mysterious about spark plugs, you just have to pick the suitable <strong>grade</strong> for <strong>your</strong> way of driving. Any brand will do nicely provided the plug reaches its temperature to burn itself clean, so forget all handbook numbers or recommendations by other bikers. You will have a look at your spark plugs to decide on the appropriate grade to keep them clean.</p><p> As to ignition advance curves, a Comet engine is not more special as any other engine, medium performance level. So why not look at any other types to see what works for them. Cooling should definitely be no factor taking into account that it has alu head, alu cylinder and reasonable finning. The combustion chamber is not too bad, in fact more modern than many contemporary types with high domed pistons in small bores of long stroke types, so no complaints here. To me a range from about 5 degrees retard and mid 30s for advanced should be quite good with higher c.r. , a very mild engine with less turbulence in the mixture will need nearer 40 degrees. A twin spark head will be happy with 30 degrees or less. To repeat myself, the familiar numbers 4 to 34 look very reasonable and plausible but I heavily question full advance way before reaching 3500 rpm. Look at any other more modern engines , not necessarily ones with the old Lucas ATDs that leave a lot to be desired. Too much advance at a too early stage will produce a hard running engine when the maximum combustion pressure meets the piston in its upward motion, nothing gained with this, possibly just excessive heat . I would do some trials with some springs in the ATD that are slightly stronger to get full advance at min. 3500 rpm, maybe better 4000 rpm. A Vincent engine is no low power side valver with a c. r. of 5 that will tolerate anything you do.</p><p></p><p> Vic</p></blockquote><p></p>
[QUOTE="oexing, post: 97094, member: 1493"] Nothing mysterious about spark plugs, you just have to pick the suitable [B]grade[/B] for [B]your[/B] way of driving. Any brand will do nicely provided the plug reaches its temperature to burn itself clean, so forget all handbook numbers or recommendations by other bikers. You will have a look at your spark plugs to decide on the appropriate grade to keep them clean. As to ignition advance curves, a Comet engine is not more special as any other engine, medium performance level. So why not look at any other types to see what works for them. Cooling should definitely be no factor taking into account that it has alu head, alu cylinder and reasonable finning. The combustion chamber is not too bad, in fact more modern than many contemporary types with high domed pistons in small bores of long stroke types, so no complaints here. To me a range from about 5 degrees retard and mid 30s for advanced should be quite good with higher c.r. , a very mild engine with less turbulence in the mixture will need nearer 40 degrees. A twin spark head will be happy with 30 degrees or less. To repeat myself, the familiar numbers 4 to 34 look very reasonable and plausible but I heavily question full advance way before reaching 3500 rpm. Look at any other more modern engines , not necessarily ones with the old Lucas ATDs that leave a lot to be desired. Too much advance at a too early stage will produce a hard running engine when the maximum combustion pressure meets the piston in its upward motion, nothing gained with this, possibly just excessive heat . I would do some trials with some springs in the ATD that are slightly stronger to get full advance at min. 3500 rpm, maybe better 4000 rpm. A Vincent engine is no low power side valver with a c. r. of 5 that will tolerate anything you do. Vic [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Comet Ignition Timing 2018
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