Here's a mystery for ya
 

91 F2
Ever run out of gas? Know that restricting/sputtering/choking sound the bike makes? Mine is making that noise now.BUTTTTT....no loss of power....ANDDDD at idle the tach is at zero and as I speed up the tach seems to read 2000 rpm's less than what it should read.The sound and tach problem occured at the same time ANNNNDDDD after I filled up.I was thinking it was just a wacky carb,but the tach issue scares me that it may be bigger.

RE: Here's a mystery for ya
 

yea i have run out of gas, and i hate that sputtering thing....my best guess is that the tach is malfunctioning or i try looking at your spark plugs because if one is not firing at all because it's dirty it might make the bike do that..but i dont know because i havent had that do it to me except for when i ran out of gas

RE: Here's a mystery for ya
 

Well,I've posted this on several forums.One guy suggested my cam tensioner was bad,which coulbe be the case...definitely have that "chainsaw sound".Im hoping he didn't mean the long strip inside the engine that the chain runs against...hope he meant the adjuster.Another guy suggested plugs...haven't checked them yet,but I went ahead and ordered some NGK Iranium plugs.Still wondering whats up with the tach?????

RE: Here's a mystery for ya
 

With your tach being weird I'd say you either have an ignition problem (source of the data for the tach) or you did jump timing some how (bad CCT, etc). F2 coils go bad after awhile, I kind of feel like thats something I'd check first.