Need help with 1980 Evinrude 150 V6 Crossfire. Starts and runs great after about 4-5 mins at WOT 6000 RPM hot horn sounds. Kill engine or return to low RPM and horn quits in about one min. VRO removed long ago runs premix. Can run all day at lower RPMs only happens above 3500 RPM. Impeller and...