Sure…that fuel miser gauge can be read just like ANY vacuum gauge…If you see flutter…could be a late opening valve…or one hanging. Hanging will make it swing…late opening a sort of flutter…almost a lost art reading those gauges. I was taught long ago and forgot more than I think I know now…Never hurts to read up and refresh…I’m not above that ever… Cant possibly store all the stuff I’ve encountered in long term memory…Info overload. Which is why I have a book to jot notes into while I am doing X, Y or Z…many X I learn many new things tackling a new issue…and I learn it while I go…just for that job…which is where the notes come in… Never be too proud to look something up…just knowing when and what to look up is a victory sometimes Grasshopper.
Its either hanging due to carbon deposits…or much more likely…opening late…because of too much valve lash. In my experience…most if not all BMW of that “vintage” need a valve adjustment…WHY? bec BMW charges an arm and a leg for it…so people skip it…so does the next owner…till you get it…all out of adjustment and sad and stuff… Just Pop the damn valve cover and get to adjusting…not a hard job…detail oriented and precise…but not hard in my book…and I have a BIG BIG book of tricks…and experience… You can do it Grasshopper, you can do it
** It sounds scary because a severely hanging valve…with smash into the rising piston doing damage to both and usually bending the valve…prob not what is happening to you…a SLIGHT hang from carbon will make the cylinder seem “sort of” dead…until rpms rise so far that you don’t notice it anymore because the compression doesn’t have the time to leak out as it does at lower RPM’s