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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Comet badly tuned or just underpowered?
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<blockquote data-quote="Tom Gaynor" data-source="post: 22621" data-attributes="member: 4034"><p>Comets are overgeared. Taking a tooth off the gearbox makes them <em>slightly</em> sprightlier. I do know someone who thinks the best way to tune a Comet is to sell it and buy a Velo Venom. There is however a good reason for there being so many 570, 600, and 650 cc Comets about, which I'm sure you can figure out. And rebuilding a Comet as 90 mm bore, giving 572 cc, is not actually much more expensive than building one standard. And those 90 bores GO, even uphill, two up, with tall Dutch people called Nobby and Ate riding them. </p><p>It sounds to me as though you have at least one fixable problem, maybe two. I think your magneto is going to glory, because it starts easy cold, but not hot. These are classic symptoms. Dave Lindsley is the man you need (see MPH). If the magneto IS going west, most other tests are misleading. If you haven't got a decent spark, then the mixture won't burn properly, and your plug will look rich. I know someone who seized a Manx Norton (ex-pen-sive...) having failed to realise it was the mag, not the main jet that gave the excess of unburnt mixture.</p><p>The second problem sounds like pinking: this suggests your spark is too far advanced. Try knocking it back to 34 deg BTDC. Time it on full advance (ATD wedged) to find out. The ATD has a nominal range of about 30 degrees, but wear increases this. So if you timed on fully retarded, i.e. not wedged, and the range was more than 30 degrees...</p><p>One last tip: if the ATD is rusted and worn, THROW THE BLOODY THING AWAY and 'phone Roy Price (MPH) to buy a new one. IMHO there are things that are simply not satisfactorily repairable, and Lucas ATD's are one of them.</p></blockquote><p></p>
[QUOTE="Tom Gaynor, post: 22621, member: 4034"] Comets are overgeared. Taking a tooth off the gearbox makes them [I]slightly[/I] sprightlier. I do know someone who thinks the best way to tune a Comet is to sell it and buy a Velo Venom. There is however a good reason for there being so many 570, 600, and 650 cc Comets about, which I'm sure you can figure out. And rebuilding a Comet as 90 mm bore, giving 572 cc, is not actually much more expensive than building one standard. And those 90 bores GO, even uphill, two up, with tall Dutch people called Nobby and Ate riding them. It sounds to me as though you have at least one fixable problem, maybe two. I think your magneto is going to glory, because it starts easy cold, but not hot. These are classic symptoms. Dave Lindsley is the man you need (see MPH). If the magneto IS going west, most other tests are misleading. If you haven't got a decent spark, then the mixture won't burn properly, and your plug will look rich. I know someone who seized a Manx Norton (ex-pen-sive...) having failed to realise it was the mag, not the main jet that gave the excess of unburnt mixture. The second problem sounds like pinking: this suggests your spark is too far advanced. Try knocking it back to 34 deg BTDC. Time it on full advance (ATD wedged) to find out. The ATD has a nominal range of about 30 degrees, but wear increases this. So if you timed on fully retarded, i.e. not wedged, and the range was more than 30 degrees... One last tip: if the ATD is rusted and worn, THROW THE BLOODY THING AWAY and 'phone Roy Price (MPH) to buy a new one. IMHO there are things that are simply not satisfactorily repairable, and Lucas ATD's are one of them. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Comet badly tuned or just underpowered?
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