I have a 2005 opti 150. this motor has ran awesome up to this point, but now it runs good until i get over around 4k rpm. when i push it past 4k-ish it spools up and after about 4-5 seconds it starts to stumble. it runs great all day below 4k. I use only 90 rec no ethanol gas. I have checked the lines from the tank to the motor all clean and solid. i am changing my fuel filter which was a bit cruddy but not sure enough to cause the problem. does anyone have any suggestions?
