On Thu, 22 Sep 2016 10:09:29 -0700 (PDT), Tim
wrote:

Surprisingly the do look pretty good for those hrs...

These EFI engines are pretty easy on plugs. Some cars can go 100,000
miles on a set of plugs. That is 3000 hours or so.
This is 1500 hours on my 60 EFI (same motor Don has)
http://gfretwell.com/ftp/1500%20hour%20plug.jpg
It is the same basic block that Yamaha uses but you see they use a
longer plug and you see the difference on the threads. It ends up
deeper in the combustion chamber. I suppose things like that and a
little better intake manifold gets it the extra few horsepower that
lets them call the same engine a 70 instead of 60. It is supposed to
bench out around 67hp. The 60 was 63 or so.
It made virtually zero difference on my boat using the same prop when
I swapped.