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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Ignition timing for twin plug heads
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<blockquote data-quote="BigEd" data-source="post: 17407" data-attributes="member: 161"><p>A few comments on my own experience with a twin plug set up on a Vincent twin.</p><p></p><p>My engine has 7.3 to 1 compression ratio, what appear to be Mk1 cams or cams reground to a similar timing and 28 mm Mikuni carburettors.</p><p>The ignition system is provided by a BT-H electronic magneto. The unit has a MK2 advance curve that has a slightly slower/longer range than early units. I have the ignition set to 32 degrees fully advanced. I use ordinary NGK plugs, grade 6-7, gapped at 18-20 thousandths of an inch.</p><p>The engine starts easily and is normally run on whatever is the cheapest petrol found at the filling station. It returns between 50 and 60 miles per imperial gallon depending how it is being ridden.</p><p>I can't comment on top speed but it cruises easily at 70 mph and with considerate use of the throttle will run at 30 mph in top, two-up. I have never heard any pinking although I do wear ear plugs when riding.</p><p>I have run it in this configuration for approximately 15,000 miles.</p><p></p><p>Some observations of my own that may or may not have any foundation:</p><p></p><p>My compression ratio is low by modern standards and as the heads are standard there are no squish bands to promote better combustion. The shape of the combustion chamber with a higher compression would probably get more benefit from a twin plug configuration.</p><p>The early BT-H twin magnetos made pre- 2007 had a slightly shorter Mk1 advance curve. I have tried the engine briefly with this earlier curve and the engine felt perhaps a little sharper so in this instance there could be some benefit in in a shorter advance range to take advantage of better flame path. This also suggest that with a higher compression and more convoluted combustion chamber a shorter advance curve might be beneficial.</p></blockquote><p></p>
[QUOTE="BigEd, post: 17407, member: 161"] A few comments on my own experience with a twin plug set up on a Vincent twin. My engine has 7.3 to 1 compression ratio, what appear to be Mk1 cams or cams reground to a similar timing and 28 mm Mikuni carburettors. The ignition system is provided by a BT-H electronic magneto. The unit has a MK2 advance curve that has a slightly slower/longer range than early units. I have the ignition set to 32 degrees fully advanced. I use ordinary NGK plugs, grade 6-7, gapped at 18-20 thousandths of an inch. The engine starts easily and is normally run on whatever is the cheapest petrol found at the filling station. It returns between 50 and 60 miles per imperial gallon depending how it is being ridden. I can't comment on top speed but it cruises easily at 70 mph and with considerate use of the throttle will run at 30 mph in top, two-up. I have never heard any pinking although I do wear ear plugs when riding. I have run it in this configuration for approximately 15,000 miles. Some observations of my own that may or may not have any foundation: My compression ratio is low by modern standards and as the heads are standard there are no squish bands to promote better combustion. The shape of the combustion chamber with a higher compression would probably get more benefit from a twin plug configuration. The early BT-H twin magnetos made pre- 2007 had a slightly shorter Mk1 advance curve. I have tried the engine briefly with this earlier curve and the engine felt perhaps a little sharper so in this instance there could be some benefit in in a shorter advance range to take advantage of better flame path. This also suggest that with a higher compression and more convoluted combustion chamber a shorter advance curve might be beneficial. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Ignition timing for twin plug heads
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