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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
1952 Comet Carburettor New Float Level.
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<blockquote data-quote="Matty" data-source="post: 47707" data-attributes="member: 1339"><p>After around 60 years and the possible effects of new additives to petrol I thought it about time that I changed the brass float and needle of what I assume is 276 carb (though Paul Richardson's book says my carb should be a 229F, whatever that is). I was also trying to cure a problem I have always had, in that the plug is always black, no matter what grades I have tried over the years - I presently use an NGK 6 grade which is pretty soft, but even this runs black and sometimes makes the bike difficult to start.</p><p></p><p>I bought the new float and needle from VOC spares and they sent a float kit for a 276 for the Comet, and on the same order I asked them to send a suitable needle jet and taper needle. They sent these last two items for a 289 and I assume they know that these will be OK for my carb.</p><p></p><p>I changed the float etc and the bike ticks over very well as it has always done - though the pilot jet setting is, and never has been very sensitive to set up and seems to work OK over a very large range of adjustment.</p><p></p><p>It was a bit more difficult to start and spat back when cold with the new plastic float, but ran well when hot. However the exhaust pipe has blued up, suggesting it is now running much weaker. The plug colour has also changed to brown now suggesting that the mixture had improved. I have checked the ignition timing and ATD which are OK</p><p></p><p> So to investigate, I have made a little adaptor to screw into the drain screw on the float chamber with a clear tube attached to be able to see the fuel levels in the float chamber.</p><p></p><p>With the old float the fuel level is roughly 1.125 inches below the top face of the float bowl without its top on, but is 1.25 inches, plus a bit, below with the new float, though the difference is probably a bit more like 3 sixteenths of an inch between the levels - so this could account for the weaker mixture.</p><p>(<em>the top of the float chamber is normally on when the levels are taken, the top of the float bowl has just been taken as a datum line)</em></p><p><em></em></p><p><em></em>I am surprised that this small level change has made such a great effect on the plug and exhaust but practically no effect on the slow running which I did not have to reset. I have also not taken the bike much over 60 mph after the change and the performance seems the same as usual, but the exhaust has blued up. Does anybody have any ideas on what might be happening please ? </p><p></p><p>Does any one know what the fuel level should be in the float chamber please for this original carb, because I seem to be "stuck between the devil and the deep blue exhaust pipe"?</p><p></p><p>I have also changed the main needle jet and slider but these have had little effect on the running which seems the same with the old or new float when the engine has warmed up. For some reason the new slider was vey tight in my old worn carb which "clinked at slow speed" as the air pulsed past. I had to lap in the new slider by several thou. before it would move up and down and it is now a beautiful fit but has not really affected the low rev end of the running in any way - the bike has always ticked over very slowly and evenly.</p><p></p><p>Hope someone can help with the expected petrol levels and can explain why I seem to have either a mixture which is too weak or plugs which are always black.</p><p></p><p>Matty - Had the bike since 1956 and it has always been used pretty regularly.</p></blockquote><p></p>
[QUOTE="Matty, post: 47707, member: 1339"] After around 60 years and the possible effects of new additives to petrol I thought it about time that I changed the brass float and needle of what I assume is 276 carb (though Paul Richardson's book says my carb should be a 229F, whatever that is). I was also trying to cure a problem I have always had, in that the plug is always black, no matter what grades I have tried over the years - I presently use an NGK 6 grade which is pretty soft, but even this runs black and sometimes makes the bike difficult to start. I bought the new float and needle from VOC spares and they sent a float kit for a 276 for the Comet, and on the same order I asked them to send a suitable needle jet and taper needle. They sent these last two items for a 289 and I assume they know that these will be OK for my carb. I changed the float etc and the bike ticks over very well as it has always done - though the pilot jet setting is, and never has been very sensitive to set up and seems to work OK over a very large range of adjustment. It was a bit more difficult to start and spat back when cold with the new plastic float, but ran well when hot. However the exhaust pipe has blued up, suggesting it is now running much weaker. The plug colour has also changed to brown now suggesting that the mixture had improved. I have checked the ignition timing and ATD which are OK So to investigate, I have made a little adaptor to screw into the drain screw on the float chamber with a clear tube attached to be able to see the fuel levels in the float chamber. With the old float the fuel level is roughly 1.125 inches below the top face of the float bowl without its top on, but is 1.25 inches, plus a bit, below with the new float, though the difference is probably a bit more like 3 sixteenths of an inch between the levels - so this could account for the weaker mixture. ([I]the top of the float chamber is normally on when the levels are taken, the top of the float bowl has just been taken as a datum line) [/I]I am surprised that this small level change has made such a great effect on the plug and exhaust but practically no effect on the slow running which I did not have to reset. I have also not taken the bike much over 60 mph after the change and the performance seems the same as usual, but the exhaust has blued up. Does anybody have any ideas on what might be happening please ? Does any one know what the fuel level should be in the float chamber please for this original carb, because I seem to be "stuck between the devil and the deep blue exhaust pipe"? I have also changed the main needle jet and slider but these have had little effect on the running which seems the same with the old or new float when the engine has warmed up. For some reason the new slider was vey tight in my old worn carb which "clinked at slow speed" as the air pulsed past. I had to lap in the new slider by several thou. before it would move up and down and it is now a beautiful fit but has not really affected the low rev end of the running in any way - the bike has always ticked over very slowly and evenly. Hope someone can help with the expected petrol levels and can explain why I seem to have either a mixture which is too weak or plugs which are always black. Matty - Had the bike since 1956 and it has always been used pretty regularly. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
1952 Comet Carburettor New Float Level.
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