Hello, I had been riding my 87 cbr600 regularly this summer, ran perfectly, all good. Went on vacation and it sat for two weeks. Now the tach reads super high at all times. It was idling at 1500 no problem, now it's like 3500. Going 50 in 4th gear with barely any gas and Im well past redline, accelerate a little and the needle is pinned.

Engine seems to be running fine, but I'm a little shy on the accelerations when the needle is pinned.

Seems more like a tach/electrical issue than mechanical. Anyone have any ideas?

Thanks|

 

Can we assume that the bike isn't actually running fast, just the tach?

 

Oh ya, I'm not assuming anything, options are either:
Tach is ok, engine is really going that fast
Tach is off, engine is fine

FWIW, when I got the bike, the tach was jumpy one it hit 7-8k it would start jumping around all over. Then it just fixed itself after a few weeks.

Bike seems to run ok. But maybe a little sluggish on acceleration. Then again I get a little gun shy to punch it when Im going 40 in 3rd gear and am already at 12k rpm.

 

Try this

 

That was my question. Those are two completely different issues. Can you tell if the bike is actually turning 12,000 rpms or does it seem to be turning normally and the tach is through the roof? I think you should be able to tell just from the sound of the bike if you are going 12,000 rpm as you ride down the road.

It sounds to me like you have a tach problem though, especially since you said the tach was a bit jumpy at one point. Stuff like that doesn't generally fix itself, although it could be intermittent as the wiring or contacts fall in and out of place.

After you've tested the tach as suggested above (although your results may be inconclusive since the tach is actually working, just not apparently working correctly) I'd disconnect the tach and see if the bike runs differently.

Sluggish acceleration, perhaps losing some ignition signal in bad tach wiring?

 

Perfect! Just what I'm loooking for. Will report back.