I have a 98 50 Hp Evinrude SPL Idles fine.But @WOT "5800 RPM's" after about 10- 15 minutes suddenly drops to about 49000rpm's then jumps bact up to 5800 "as though the throttle was pulled backand then pushed right back to wot" also when @ 4600 rpm's it happens but it's not such a drop in rpm's...