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Dual spark plug mod
I have a old '63 Iron head sporster that I am restoring. I am being told by the "experts" that because of the high dome piston design detonation will be a problem because of the low lead gas unless I modify the heads to accept two plugs plus buy a special spark coil that will handle the additional plugs. I also am advised to change out the valve seats to low lead type.
I am also restroring a 61 pre unit Bonnie. The pistons on the Bonnie look just like the old sporster and compression is 9:1 for both engines. It seems to me that if detonation is a problem on the sporster it will be problem on the Bonnie as well. There are plenty of threads and discussion on this forum dealing with the need to install low lead seats, but I have seen nothing about the need for dual plugs/cylinder so I figure it isn't a problem but not sure why. Of course the sporster is a V twin rather than a vertical twin, so is that the difference?
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