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Old 09-09-2008, 07:24 PM
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At 5300 rpm it sounds like you are right into it with the secondaries wide open, have you tried going up one jet size on the secondaries? I would do a plug chop at rpm to see what you are getting for mixture at high rpm.

Colder plugs likely won't solve the problem unless you are really lean at which point a jet change on the secondaries should solve that.

10.75 is pretty high for a street motor, not much you can do about the poor fuel quality either so you might want to consider putting in a thicker head gasket or running fuel treatment or a gallon of race gas at each fill up.
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