Mystery noise solved (kind of)

Last year after I rebuilt just about everything on my motorcycle a loud noise popped up that increased in pitch when I revved the engine. My friend said I got a cat stuck in the air box when I rebuilt it. It was very sporatic, maybe a bit after i started, but would go away quick, so i could never track it down. I though it was the starter motor not disengaging, or maybe a hole in my pipes or something.
recently on a 3 hour ride back home I was taking an exit and the noise came back, and it would not stop. Finally I was able to track it to the tachometer. I only had about 30 miles to home so I let it go (dumb dumb). must have broken a tooth on a gear and it was just whining and got worse.
about 2 miles from home it shoots up to 12000 rpm (hand off throttle, just the gadges), holds there then something strait out of exorcist it spins around so fast it snaps the needle, and just keeps spinning. now it sits at 5000 with a stubby needle.

anyone have a spare I can buy, and maybe knows what happened?

 

Seca 550 cluster removal and breakdown: http://xjbikes.com/Forums/viewtopic/t=14948.html

Yamaha mechanical instrument tech: http://xjbikes.com/Forums/viewtopic/t=15303.html

Losing the 85mph silliness while you're in there: http://xjbikes.com/Forums/viewtopic/t=22823.html

Some things of interest to 550 Seca owners: http://xjbikes.com/Forums/viewtopic/t=36235.html

My '83 550 Seca has been stone reliable since I put it back on the road three seasons and 10K miles ago. Oil changes, spark plugs, valve clearance checks and a rear tire. That's it.