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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Air Fuel Gauge 02 Sensor Lambda Sensor
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<blockquote data-quote="Magnetoman" data-source="post: 107879" data-attributes="member: 2806"><p>Warning: Vincents use Amals, and this post deals with jetting an Amal aided by an air/fuel meter, but other than that it has nothing whatever to do with Vincents</p><p></p><p>I've been tied up with other projects the last couple of weeks but yesterday returned to jetting. The background is I'm trying to determine the minimum modifications needed to make a 2-stroke 1000-Series Amal Concentric work with a 500 cc Gold Star.</p><p></p><p>Yesterday I only had time to make a quick jetting run from which I determined the AFR was 10:1 at full throttle with its 290 main jet. From that I calculated to decrease it to get to 12:1 would require dropping the main jet to 10/12 x 290 = 241.7. Or, that using a 240 would give 290/240 x 10 = 12.08:1. However, after looking at today's results, which I'll discuss momentarily, I looked again at yesterday's, shown in the first graph. The fat green line shows where an AFR of 9.4 would be. Note that I was at full throttle yesterday for only ~2 sec. so it's possible the thin green line would have reached 9.4 in another second. Make a mental note of that.</p><p></p><p>OK, turning to today's results, and remembering that maximum engine power should be achieved when the AFR is in the range ~12-13, the second graph shows that with it held at ~1/8 throttle the AFR was 12.3:1. So far, so good.</p><p></p><p>The third graph shows that at ~1/3 throttle, where basically every variable in the carburetor is contributing, the AFR drops a bit to 12.0:1. Still, so far, so good. However, the graph also shows that at full throttle it drops to 11.0:1 despite my above calculation that it should have been 12.08:1. I'll return to this in a moment making use of the mental note you made two paragraphs ago.</p><p></p><p>The fourth graph shows that the second full-throttle run today resulted in a slightly higher 11.4:1 than the first run. However, note that it took 2-3 seconds for the ratio to drop to that value.</p><p></p><p>I used 10:1 from yesterday's run to calculate that I should use a 240 main jet today. Referring back to the first graph, if instead I had been able to hold full throttle for 2 sec. longer, and if the AFR had dropped to 9.4 in that time, then today with the 240 main jet the AFR should have been 11.36:1 at full throttle, which it was. That is, within experimental error the calculation I did yesterday to arrive at 240 gave the "correct" answer. However the "experiment" I did upon which I based the calculation wasn't run for long enough to achieve the steady state AFR value. The important point from this is that not only does the air/fuel meter tell you the AFR with the current configuration of the carburetor, if you run the tests for more than ~2 seconds it <em>quantitatively</em> tells you what changes to make to achieve the desired final result.</p><p></p><p>In light of today's longer full throttle runs, and using 11.0-11.4:1 as the values they gave, changing to a 220 for the next run should give 12.0-12.4:1. The smaller main jet also will increase the AFR somewhat at partial throttle resulting in values at all throttle settings falling in the sweet spot of 12-13:1 that gives maximum power.</p><p></p><p>As an aside, the jetting I used yesterday and today felt perfect at all throttle settings and rapid changes in throttle positions. At least, to within my ability to run full throttle tests on a Gold Star in an urban setting. Without the Innovate A/F meter I would have been happy with yesterday's 290 main jet, or with today's 240, even though it looks like 220 will be the one to use. Also, all of these settings are rich compared with stoichiometric 14.7:1. If I were tuning for economy rather than performance I'm not sure I could achieve it across the range with the present 2-stroke spray tube and air compensating passage that are part of all 1000-Series Concentrics (although, both can be changed). Certainly not with a .106 needle jet. </p><p>[ATTACH]27347[/ATTACH] [ATTACH]27348[/ATTACH] [ATTACH]27347[/ATTACH] [ATTACH]27347[/ATTACH]</p></blockquote><p></p>
[QUOTE="Magnetoman, post: 107879, member: 2806"] Warning: Vincents use Amals, and this post deals with jetting an Amal aided by an air/fuel meter, but other than that it has nothing whatever to do with Vincents I've been tied up with other projects the last couple of weeks but yesterday returned to jetting. The background is I'm trying to determine the minimum modifications needed to make a 2-stroke 1000-Series Amal Concentric work with a 500 cc Gold Star. Yesterday I only had time to make a quick jetting run from which I determined the AFR was 10:1 at full throttle with its 290 main jet. From that I calculated to decrease it to get to 12:1 would require dropping the main jet to 10/12 x 290 = 241.7. Or, that using a 240 would give 290/240 x 10 = 12.08:1. However, after looking at today's results, which I'll discuss momentarily, I looked again at yesterday's, shown in the first graph. The fat green line shows where an AFR of 9.4 would be. Note that I was at full throttle yesterday for only ~2 sec. so it's possible the thin green line would have reached 9.4 in another second. Make a mental note of that. OK, turning to today's results, and remembering that maximum engine power should be achieved when the AFR is in the range ~12-13, the second graph shows that with it held at ~1/8 throttle the AFR was 12.3:1. So far, so good. The third graph shows that at ~1/3 throttle, where basically every variable in the carburetor is contributing, the AFR drops a bit to 12.0:1. Still, so far, so good. However, the graph also shows that at full throttle it drops to 11.0:1 despite my above calculation that it should have been 12.08:1. I'll return to this in a moment making use of the mental note you made two paragraphs ago. The fourth graph shows that the second full-throttle run today resulted in a slightly higher 11.4:1 than the first run. However, note that it took 2-3 seconds for the ratio to drop to that value. I used 10:1 from yesterday's run to calculate that I should use a 240 main jet today. Referring back to the first graph, if instead I had been able to hold full throttle for 2 sec. longer, and if the AFR had dropped to 9.4 in that time, then today with the 240 main jet the AFR should have been 11.36:1 at full throttle, which it was. That is, within experimental error the calculation I did yesterday to arrive at 240 gave the "correct" answer. However the "experiment" I did upon which I based the calculation wasn't run for long enough to achieve the steady state AFR value. The important point from this is that not only does the air/fuel meter tell you the AFR with the current configuration of the carburetor, if you run the tests for more than ~2 seconds it [i]quantitatively[/i] tells you what changes to make to achieve the desired final result. In light of today's longer full throttle runs, and using 11.0-11.4:1 as the values they gave, changing to a 220 for the next run should give 12.0-12.4:1. The smaller main jet also will increase the AFR somewhat at partial throttle resulting in values at all throttle settings falling in the sweet spot of 12-13:1 that gives maximum power. As an aside, the jetting I used yesterday and today felt perfect at all throttle settings and rapid changes in throttle positions. At least, to within my ability to run full throttle tests on a Gold Star in an urban setting. Without the Innovate A/F meter I would have been happy with yesterday's 290 main jet, or with today's 240, even though it looks like 220 will be the one to use. Also, all of these settings are rich compared with stoichiometric 14.7:1. If I were tuning for economy rather than performance I'm not sure I could achieve it across the range with the present 2-stroke spray tube and air compensating passage that are part of all 1000-Series Concentrics (although, both can be changed). Certainly not with a .106 needle jet. [ATTACH]27347[/ATTACH] [ATTACH]27348[/ATTACH] [ATTACH]27347[/ATTACH] [ATTACH]27347[/ATTACH] [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Air Fuel Gauge 02 Sensor Lambda Sensor
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