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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Big Carburettors
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<blockquote data-quote="Magnetoman" data-source="post: 106339" data-attributes="member: 2806"><p>At the risk of going off topic, on a ride through Texas last year my Catalina Gold Star shed its silencer. Once back home I installed a replacement but the bike ran horribly. Making a long story short, with the air cleaner removed the bike ran fine, but a visible cloud of air/fuel pulsed from the inlet at idle. That ejected pulse had traveled over the spray tube on its way back out and drawn additional fuel into the mixture, but enough of the rich mixture escaped into the open air that when the remainder of the cloud was sucked back in (diluted with fresh air), and despite the third pass over the spray tube, the mixture was lean enough (or, not-incredibly-rich enough) that the bike ran OK. But, with the air cleaner attached the over-rich ejected cloud wasn't able to be diluted and the bike ran horribly. Once I discovered the problem I solved it by drilling holes in the baffle of the replacement silencer to reduce the back pressure that was pushing the mixture back out the carburetor during the large overlap of the inlet and exhaust cam. </p><p></p><p>Since we're already a bit off topic, some of you might be interested in some <a href="http://www.britbike.com/forums/ubbthreads.php/topics/770338/re-correct-needle-for-1000-series-concentrics#Post770338" target="_blank">recent flow bench results</a>. My search for data on spray tubes or flow bench data on Amal carburetors in general turned up nothing so I believe this is the only flow bench data of its type is to be found in print or on the web. It's relevant for anyone thinking of using a 1000-Series Concentric since most are in 2-stroke configuration.</p></blockquote><p></p>
[QUOTE="Magnetoman, post: 106339, member: 2806"] At the risk of going off topic, on a ride through Texas last year my Catalina Gold Star shed its silencer. Once back home I installed a replacement but the bike ran horribly. Making a long story short, with the air cleaner removed the bike ran fine, but a visible cloud of air/fuel pulsed from the inlet at idle. That ejected pulse had traveled over the spray tube on its way back out and drawn additional fuel into the mixture, but enough of the rich mixture escaped into the open air that when the remainder of the cloud was sucked back in (diluted with fresh air), and despite the third pass over the spray tube, the mixture was lean enough (or, not-incredibly-rich enough) that the bike ran OK. But, with the air cleaner attached the over-rich ejected cloud wasn't able to be diluted and the bike ran horribly. Once I discovered the problem I solved it by drilling holes in the baffle of the replacement silencer to reduce the back pressure that was pushing the mixture back out the carburetor during the large overlap of the inlet and exhaust cam. Since we're already a bit off topic, some of you might be interested in some [URL='http://www.britbike.com/forums/ubbthreads.php/topics/770338/re-correct-needle-for-1000-series-concentrics#Post770338']recent flow bench results[/URL]. My search for data on spray tubes or flow bench data on Amal carburetors in general turned up nothing so I believe this is the only flow bench data of its type is to be found in print or on the web. It's relevant for anyone thinking of using a 1000-Series Concentric since most are in 2-stroke configuration. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Big Carburettors
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