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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Concentric Mk1's on a twin - problems!
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<blockquote data-quote="b.l.hayward@tesco.net" data-source="post: 27033" data-attributes="member: 865"><p><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Times New Roman'"><strong>Background</strong>: Rebuilt twin engine using new parts only where necessary; currently completed just over 100 miles; fitted with 30mm Mk1 Concentrics 930 – settings: pilot 25; needle jet 106; main jet 200; needle no ? (no markings); needle clip position = middle and bottom groove (no difference with problem – see later); slide 3. Am using 2 left-hand concentrics. Refurbished magneto ignition. Also noted that the inlet port dia is 34mm (carb choke is 30mm). The carbs, top end and bottom end are not related and were purchased separately!</span></span></span></p><p><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Times New Roman'"><strong>Symptoms: </strong>Engine starts easily and at and just above tick over seems to run on one cylinder (the front – no 2). When I try to pick up the motor with a slight throttle opening, No 1 cylinder (the rear) spits back thru carb and often ‘bangs’ in the exhaust. If I close the air lever it stops and both cylinders seem to fire as normal – open the choke and the spitting/banging in No1 returns. No1 cylinder gets much hotter and quicker than No2 and the exhaust pipe (chrome) is blueing. If I open the throttle more than 1/8 the spitting/banging stops and all seems well (but is it?).</span></span></span></p><p><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Times New Roman'"><strong>My Original Conclusion: </strong>Weak mixture in cylinder 1 in the pilot phase.</span></span></span></p><p><strong><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"><span style="color: #000000">Actions So Far: </span></span></span></strong> <ol> <li data-xf-list-type="ol"><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"><span style="color: #000000">check ignition timing – ok</span></span></span></li> <li data-xf-list-type="ol"><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"><span style="color: #000000">check for air leaks carb/stub and stub/head – none</span></span></span></li> <li data-xf-list-type="ol"><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"><span style="color: #000000">replace concentric ‘O’ ring – no change</span></span></span></li> <li data-xf-list-type="ol"><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"><span style="color: #000000">screw in pilot air screw all the way (richest position) – no change</span></span></span></li> <li data-xf-list-type="ol"><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"><span style="color: #000000">remove pilot jet – no change</span></span></span></li> <li data-xf-list-type="ol"><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"><span style="color: #000000">move needle clip to lowest (richest) position – no change</span></span></span></li> <li data-xf-list-type="ol"><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"><span style="color: #000000">check pilot air/petrol passages are clear – done but no change </span></span></span></li> <li data-xf-list-type="ol"><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"><span style="color: #000000">petrol flow to carb – ok (tickler floods).</span></span></span></li> </ol><p><strong><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Times New Roman'">Thoughts: </span></span></span></strong> <ol> <li data-xf-list-type="ol"><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"><span style="color: #000000">verify that I have the right needle – what no. should it be and would this really make a difference early in the slide opening range? </span></span></span></li> <li data-xf-list-type="ol"><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"><span style="color: #000000">try a ‘richer’ slide – 2 ½?</span></span></span></li> </ol><p><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Times New Roman'"><strong>Help!: </strong>Any other thoughts on problem and likely solution gratefully received. I am baffled!</span></span></span></p></blockquote><p></p>
[QUOTE="b.l.hayward@tesco.net, post: 27033, member: 865"] [SIZE=3][COLOR=#000000][FONT=Times New Roman][B]Background[/B]: Rebuilt twin engine using new parts only where necessary; currently completed just over 100 miles; fitted with 30mm Mk1 Concentrics 930 – settings: pilot 25; needle jet 106; main jet 200; needle no ? (no markings); needle clip position = middle and bottom groove (no difference with problem – see later); slide 3. Am using 2 left-hand concentrics. Refurbished magneto ignition. Also noted that the inlet port dia is 34mm (carb choke is 30mm). The carbs, top end and bottom end are not related and were purchased separately![/FONT][/COLOR][/SIZE] [SIZE=3][COLOR=#000000][FONT=Times New Roman][B]Symptoms: [/B]Engine starts easily and at and just above tick over seems to run on one cylinder (the front – no 2). When I try to pick up the motor with a slight throttle opening, No 1 cylinder (the rear) spits back thru carb and often ‘bangs’ in the exhaust. If I close the air lever it stops and both cylinders seem to fire as normal – open the choke and the spitting/banging in No1 returns. No1 cylinder gets much hotter and quicker than No2 and the exhaust pipe (chrome) is blueing. If I open the throttle more than 1/8 the spitting/banging stops and all seems well (but is it?).[/FONT][/COLOR][/SIZE] [SIZE=3][COLOR=#000000][FONT=Times New Roman][B]My Original Conclusion: [/B]Weak mixture in cylinder 1 in the pilot phase.[/FONT][/COLOR][/SIZE] [B][FONT=Times New Roman][SIZE=3][COLOR=#000000]Actions So Far: [/COLOR][/SIZE][/FONT][/B][LIST=1] [*][FONT=Times New Roman][SIZE=3][COLOR=#000000]check ignition timing – ok[/COLOR][/SIZE][/FONT] [*][FONT=Times New Roman][SIZE=3][COLOR=#000000]check for air leaks carb/stub and stub/head – none[/COLOR][/SIZE][/FONT] [*][FONT=Times New Roman][SIZE=3][COLOR=#000000]replace concentric ‘O’ ring – no change[/COLOR][/SIZE][/FONT] [*][FONT=Times New Roman][SIZE=3][COLOR=#000000]screw in pilot air screw all the way (richest position) – no change[/COLOR][/SIZE][/FONT] [*][FONT=Times New Roman][SIZE=3][COLOR=#000000]remove pilot jet – no change[/COLOR][/SIZE][/FONT] [*][FONT=Times New Roman][SIZE=3][COLOR=#000000]move needle clip to lowest (richest) position – no change[/COLOR][/SIZE][/FONT] [*][FONT=Times New Roman][SIZE=3][COLOR=#000000]check pilot air/petrol passages are clear – done but no change [/COLOR][/SIZE][/FONT] [*][FONT=Times New Roman][SIZE=3][COLOR=#000000]petrol flow to carb – ok (tickler floods).[/COLOR][/SIZE][/FONT] [/LIST][B][SIZE=3][COLOR=#000000][FONT=Times New Roman]Thoughts: [/FONT][/COLOR][/SIZE][/B][LIST=1] [*][FONT=Times New Roman][SIZE=3][COLOR=#000000]verify that I have the right needle – what no. should it be and would this really make a difference early in the slide opening range? [/COLOR][/SIZE][/FONT] [*][FONT=Times New Roman][SIZE=3][COLOR=#000000]try a ‘richer’ slide – 2 ½?[/COLOR][/SIZE][/FONT] [/LIST][SIZE=3][COLOR=#000000][FONT=Times New Roman][B]Help!: [/B]Any other thoughts on problem and likely solution gratefully received. I am baffled![/FONT][/COLOR][/SIZE] [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Concentric Mk1's on a twin - problems!
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