Hi. My FZJ80 has had a high pitched whistling noise for some time (not when I first bought it). It only occurs on acceleration, in any gear, whether it be light, moderate acceleration or wide open throttle and only above 2.5k rpm (roughly).
I'm thinking it's a vacuum leak somewhere. I have tried listening with a length of hose and tried systematically spraying potential areas with Aerostart.
I've been unsuccessful in remedying the issue (though I did find some other split hoses).