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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Tuning - Original Comet Carb and LM-1 AFR Meter
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<blockquote data-quote="Tom Gaynor" data-source="post: 13800" data-attributes="member: 4034"><p><strong>Jetting Comets</strong></p><p></p><p>I run standard 289's, but the carbs have been sleeved, so I can't buy replacements off the shelf. If I could, I might try 3 1/2 slides, but since the backfiring stops within half a mile, and getting a pair of custom 3 1/2's made is just too much hassle, I'll let lethargy triumph.</p><p>(The classic method of setting fuelling on Manx Nortons, which in use are run mainly wide open, is to lean them out until they pop on the over-run, then richen them one. Plugs are "dark white" when mixture is correct. With the almost universal Gardner flat-slide carbs, that means clicking the needle down until it pops, then clicking it up one. No spanners involved.) </p><p>Just make sure that there's enough head space under the slide to clear the jet block, before converting 4 to 3 1/2, but I have successfully "converted" a 276 #4 to #3 with no problem. Did it with hand tools too, a Junior hacksaw and a file!</p><p>After much buggering about, I'm currently running stock settings. 180 jets, #4 slides, needle 4 grooves from top (i.e. rich). What I had been doing was trying to cure unrelated faults through carburation. I had worn guides, and most critically, the front float level was about 1/8" too high. Then it occurred to me (sounds pretty dim) that if all the settings were the same, and the front plug was STILL sooty, it had to be float level. Which Sid Biberman had told me months before was important. With the bike tilted over about 5 degrees in the direction of the pilot, fuel should JUST weep out of the pilot jet hole. (Screw out, of course.)</p><p>Bon chance...</p><p></p><p>Tom</p></blockquote><p></p>
[QUOTE="Tom Gaynor, post: 13800, member: 4034"] [b]Jetting Comets[/b] I run standard 289's, but the carbs have been sleeved, so I can't buy replacements off the shelf. If I could, I might try 3 1/2 slides, but since the backfiring stops within half a mile, and getting a pair of custom 3 1/2's made is just too much hassle, I'll let lethargy triumph. (The classic method of setting fuelling on Manx Nortons, which in use are run mainly wide open, is to lean them out until they pop on the over-run, then richen them one. Plugs are "dark white" when mixture is correct. With the almost universal Gardner flat-slide carbs, that means clicking the needle down until it pops, then clicking it up one. No spanners involved.) Just make sure that there's enough head space under the slide to clear the jet block, before converting 4 to 3 1/2, but I have successfully "converted" a 276 #4 to #3 with no problem. Did it with hand tools too, a Junior hacksaw and a file! After much buggering about, I'm currently running stock settings. 180 jets, #4 slides, needle 4 grooves from top (i.e. rich). What I had been doing was trying to cure unrelated faults through carburation. I had worn guides, and most critically, the front float level was about 1/8" too high. Then it occurred to me (sounds pretty dim) that if all the settings were the same, and the front plug was STILL sooty, it had to be float level. Which Sid Biberman had told me months before was important. With the bike tilted over about 5 degrees in the direction of the pilot, fuel should JUST weep out of the pilot jet hole. (Screw out, of course.) Bon chance... Tom [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Tuning - Original Comet Carb and LM-1 AFR Meter
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