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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
New Amal Premier 900 series Carb for Comets
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<blockquote data-quote="Martyn Goodwin" data-source="post: 48624" data-attributes="member: 2433"><p><strong>Update Jan 8, 2014</strong>.</p><p></p><p>Given that the advise I received in December was that the earlier piston failure was due to detonation and not running lean I have been experimenting - at first with ignition timing and them with main jet size. Still no luck in getting dyno time so its still seat of the pants testing.</p><p></p><p>I changed the timing from 32 BTDC down to 30 BTDC (fully advanced) and found a improvement. So I did it again, this time stepping down to 28 BTDC, which BTW seems to be the full advance setting that Pazon use in their fully electronic system for a Comet. At 28 BTDC there seemed to be a further performance improvement. </p><p></p><p>It must be noted that I am using the Lucas Magneto and a mechanical ATD - the ATD would normally provide a range of 34 degrees from full advance to full retard. With my ATD I have bent its "ears" reducing its range to 30 degrees. What this means is with 28 BTDC fully advanced, retarded its at 2 ATDC when starting - it also means the when at low speed or at idle the engine is running around 6 degrees more retarded that the original design spec. of 4 BTDC fully retarded.</p><p></p><p>So with 28 BTDC fully advanced and 2 ATDC fully retarded I commenced further experiments , this time with the main jet. I changed down just one jet size at a time then did an extended run of around 200 miles. With a 230 main performance seemed better than with the 240 - especially high speed performance and pulling power on hills. With the 230 in place there was no noticeable "blueing" of the exhaust system.</p><p></p><p>I then changed over to a 220 main followed by another 200 mile day ride. Top end performance seems just a whisker better as did the performance on hills, though this time I did notice a slight blueing of the exhaust within the first 4 to 6 inches from the head. I am thinking (feedback is encouraged chaps!) that this Bluing may be happening because these the flame front is travelling down the exhaust pipe when the exhaust valve is open - so I have now reset my ignition to 31 BTDC fully advanced (it was 28 BTDC) which equates to 1 BTDC fully retarded.</p><p></p><p>Further road testing is scheduled for tomorrow.</p><p></p><p>Martyn</p></blockquote><p></p>
[QUOTE="Martyn Goodwin, post: 48624, member: 2433"] [B]Update Jan 8, 2014[/B]. Given that the advise I received in December was that the earlier piston failure was due to detonation and not running lean I have been experimenting - at first with ignition timing and them with main jet size. Still no luck in getting dyno time so its still seat of the pants testing. I changed the timing from 32 BTDC down to 30 BTDC (fully advanced) and found a improvement. So I did it again, this time stepping down to 28 BTDC, which BTW seems to be the full advance setting that Pazon use in their fully electronic system for a Comet. At 28 BTDC there seemed to be a further performance improvement. It must be noted that I am using the Lucas Magneto and a mechanical ATD - the ATD would normally provide a range of 34 degrees from full advance to full retard. With my ATD I have bent its "ears" reducing its range to 30 degrees. What this means is with 28 BTDC fully advanced, retarded its at 2 ATDC when starting - it also means the when at low speed or at idle the engine is running around 6 degrees more retarded that the original design spec. of 4 BTDC fully retarded. So with 28 BTDC fully advanced and 2 ATDC fully retarded I commenced further experiments , this time with the main jet. I changed down just one jet size at a time then did an extended run of around 200 miles. With a 230 main performance seemed better than with the 240 - especially high speed performance and pulling power on hills. With the 230 in place there was no noticeable "blueing" of the exhaust system. I then changed over to a 220 main followed by another 200 mile day ride. Top end performance seems just a whisker better as did the performance on hills, though this time I did notice a slight blueing of the exhaust within the first 4 to 6 inches from the head. I am thinking (feedback is encouraged chaps!) that this Bluing may be happening because these the flame front is travelling down the exhaust pipe when the exhaust valve is open - so I have now reset my ignition to 31 BTDC fully advanced (it was 28 BTDC) which equates to 1 BTDC fully retarded. Further road testing is scheduled for tomorrow. Martyn [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
New Amal Premier 900 series Carb for Comets
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