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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Starts, runs then slowly "chokes up"
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<blockquote data-quote="timetraveller" data-source="post: 110242" data-attributes="member: 456"><p>Going back to doctires original posting it seems to me that the most significant thing is that the bike runs well for twenty miles. That rules out anything to do with inlet ports, carb defects and so on. In twenty miles it will have used all the fuel in the fuel pipes etc and will have had to take fuel from above the taps. We are left with three possibilities, fuel supply, ignition or some unusual mechanical problem wherein something which starts off tight and well adjusted becomes loose and no longer doing what it should. It seems not to be restricted fuel flow, (eg blocked tank vent, dirty filters on the petrol taps etc). If it was a failing coil or condenser then that would be easily checked by testing to see what strength of spark there is immediately after limping home as compared with the spark when the bike has been sat overnight. Assuming the strength of the spark is satisfactory then it would seem impossible that something was slipping (eg bob weights, drive to distributor, etc) as then there would be nothing to get that mechanical fault to re-align itself when the bike was cooling down. If all these items have been checked then there has to be something mechanical which when it gets hot causes the fault. If you turn the engine over slowly as soon as you get home, with the fault, is there a noise present which is not there when the engine is cold. Is the compression the same with the fault as without? I'm thinking sticky valves, valve collars moving when hot and then going back to their correct position while cooling down.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 110242, member: 456"] Going back to doctires original posting it seems to me that the most significant thing is that the bike runs well for twenty miles. That rules out anything to do with inlet ports, carb defects and so on. In twenty miles it will have used all the fuel in the fuel pipes etc and will have had to take fuel from above the taps. We are left with three possibilities, fuel supply, ignition or some unusual mechanical problem wherein something which starts off tight and well adjusted becomes loose and no longer doing what it should. It seems not to be restricted fuel flow, (eg blocked tank vent, dirty filters on the petrol taps etc). If it was a failing coil or condenser then that would be easily checked by testing to see what strength of spark there is immediately after limping home as compared with the spark when the bike has been sat overnight. Assuming the strength of the spark is satisfactory then it would seem impossible that something was slipping (eg bob weights, drive to distributor, etc) as then there would be nothing to get that mechanical fault to re-align itself when the bike was cooling down. If all these items have been checked then there has to be something mechanical which when it gets hot causes the fault. If you turn the engine over slowly as soon as you get home, with the fault, is there a noise present which is not there when the engine is cold. Is the compression the same with the fault as without? I'm thinking sticky valves, valve collars moving when hot and then going back to their correct position while cooling down. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Starts, runs then slowly "chokes up"
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