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Joined: Oct 2006
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Leigh Offline OP
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I've done 30 km on a 1969 BSA Lightning which has just been overhauled.
The right-hand exhaust is discoloured to about halfway down the left has a slight yellow blush about what I would expect.

Ive checked the carburettors and everything looks ok jets the same and needle heights the same, floats ok, new float needles and gaskets.

It has electronic ignition and a single double wound coil.
The plug was a lighter grey than the left but not really white.

Its got me stumped

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Maybe an intake air leak leaning it out?


1970 T120R - 'Anton'
1970 Commando - 'Bruno'
1967 T120R - 'Caesar'
1968 Lightning - 'Dora'
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Originally Posted by Hugh Jörgen
Maybe an intake air leak leaning it out?

+1

What's the idle like? Lumpy, smooth, even?
Have you put a strobe on it? If it's EI chack it at 4k+

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Check carb synch, if RHS is working harder it may be LHS is lagging on opening.


71 Devimead, John Hill, John Holmes A65 750
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It’s possible that the needle jet might not be quite the right size, a test for these will be to swap the complete jet holder including the two jets from right side to left.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
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I've tried to avoid more than one carb on any bike to lessen the variables. That said, I've read many times if you have multi carbs you should tune them so they work on the cylinder they are attached to. That means they will not necessarily have the same jets, needle clip position, etc. Slides need to be synchronized but beyond that do what you have to do to make it work.


Laurence Luce
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Situations like these I swap ignition leads first. Second check for vacuum leaks. Then compression, then valve adjustment, carbs last.
Hope this helps

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Thanks Guys, It gives me something to be going on with


Moderated by  Allan G, Jon W. Whitley 

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