The existing NGK plugs look a bit average so I thought I'd replace them. Was rather gobsmacked when I discovered these plugs are $20 each here in Oz. Seems a bit odd that a low tech and low performance motor should require such expensive performance plugs. They are long life plug but that's not such a great thing if they're left in the head for too long in 1.3 Endura .
Has anyone tried a less expensive alternative with the same heat rating etc as the NGK PTR5D?
Is there some technical reason why this motor needs these high spec plugs?
Look forward to the wisdom.