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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Ignition Advance
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<blockquote data-quote="greg brillus" data-source="post: 128534" data-attributes="member: 597"><p>Several things to look at there...... so you have the initial advance point (or full retard) the max overall advance and the perhaps the one that is overlooked most, is the rate of change of the advance. It is this rate of change that is the dangerous one.......on a lot of old bikes and cars for that matter, the advance mechanisms are not only worn, but the spring rates that control this are all over the place. I had a late model Velo here that the owner basically cooked the engine........on closer inspection I found the original BTH advance unit was going to full advance way too soon. So even with the advance set to say 4 or 5 degrees BTDC for good starting and a max advance of say 32 to 34 degrees full advance, on a ride around the block, up and down some of my local hills......The engine would ping at anything approaching 1/2 throttle in say 3rd or top gear without even trying.........after some careful rework of the advance unit return spring which was very weak in it's action, this immediately transformed the bike and the detonation near stopped unless you really worked the engine hard on an incline in top gear.......In these instances you are better off to use a slightly higher octane fuel if this is available........ I never recommend using 98 octane fuel here unless the bike is used very regularly as i feel it is more suited to modern fully enclosed fuel systems where the top end volatile properties of the fuel are held........If that fuel is left for 2 to 3 months in an old bike, or car, the fuel quickly becomes reduced to near kerosene, or not much better.</p></blockquote><p></p>
[QUOTE="greg brillus, post: 128534, member: 597"] Several things to look at there...... so you have the initial advance point (or full retard) the max overall advance and the perhaps the one that is overlooked most, is the rate of change of the advance. It is this rate of change that is the dangerous one.......on a lot of old bikes and cars for that matter, the advance mechanisms are not only worn, but the spring rates that control this are all over the place. I had a late model Velo here that the owner basically cooked the engine........on closer inspection I found the original BTH advance unit was going to full advance way too soon. So even with the advance set to say 4 or 5 degrees BTDC for good starting and a max advance of say 32 to 34 degrees full advance, on a ride around the block, up and down some of my local hills......The engine would ping at anything approaching 1/2 throttle in say 3rd or top gear without even trying.........after some careful rework of the advance unit return spring which was very weak in it's action, this immediately transformed the bike and the detonation near stopped unless you really worked the engine hard on an incline in top gear.......In these instances you are better off to use a slightly higher octane fuel if this is available........ I never recommend using 98 octane fuel here unless the bike is used very regularly as i feel it is more suited to modern fully enclosed fuel systems where the top end volatile properties of the fuel are held........If that fuel is left for 2 to 3 months in an old bike, or car, the fuel quickly becomes reduced to near kerosene, or not much better. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Ignition Advance
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