All the current posts are old due to the site rebuild, but we need to "wake up the forum" so will add a comment here.
As a general rule using WI slows down the fuel burn slightly. On a properly set up system most folks need an additional 2-3 degrees advance when they are spraying water.
If you need significantly more advance than that to avoid high rpm missfire, you may be spraying too much water at high rpm. You might want to back off the spray rate slightly at high rpm and see if the missfire goes away. You might also have a spray mix distribution problem that is not giving a uniform mixture at high rpm.
Larry
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