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Triumph workshop manual has a section on how to read plugs. They state that left side plug should be read to adjust carbs and that right side should be darker. This is true on my bike. Right side has more black that left. Any thoughts on why this should be.
 

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arghh!!!some say ,and they maybe right,that the left cylinder is running hotter than the right one.in fact most of the engine seizure occurs on the left cylinder .i heard that it was because the left cylinder gets less oil splashed from the big end bearing as the oil feed is on the right side of the crank.why not?
anyway the difference should be light if you have a well settled ignition(a few degrees changes it all)and if your carbs are correcly tuned(with twin carbs you have to check carefully each air screw as states by the manual.
hope i was clear.these engines are very sensible to timing and carb tuning
ben
 

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With my Tiger head, the 68 runs both plugs identical, or as close to identical as I can tell.
With the 70 and later bikes, with the crankcase breathing through the left main bearing, there is a lot of oil activity on that side, too. So some is picked up by the left chop and thrown around and up onto the cylinder wall.
Some of the 78 T140s had splay port heads, some parallel port. The parallel port heads with the MK2 concentrics are closer to the Tiger head in structure, so I would think that any difference in mixture strength for these would lie with the carbs (using the similarity of the plugs from my Tiger head)....some difference caused by the handing of the carb, or something like that. Logically, that should also apply to the splay port head, unless some obscure physics principle comes into play.....
 
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