Speedometer Question.mx

Well, hi to everyone...
A friend and I run a small bike shop in the center of Mexico, and I always find the posts I have read here rather useful...
Which takes me to making this question..
I own a 00'929 and the bike began giving us a series of problems during the last 5 weeks, we changed the stator, rectifier, clutch ass, had to send the injectors to the lab, replace the battery, fuel pump, pressure reg... Oh well, the bike had 50,000 kms. when we "rescued" it from a rather reckless, neglectful rider...
anyway, she's fine now, and runs great...
Xcept for this thing:
I start the bike either in the morning or afternoon, and wait for it to warm up a little, then I hit the boulevard, after what i think is a minute, the speedometer reads 0kms/hr then it goes something as 40kms/hr, then 66kms/hr, then 100kms/hr, then it goes back to zero, then the reading goes back to normal (which i assume given the comparing my speed to other vehicles on the road).
Sometimes the bike acts as if the fuel didn't reach the pistons, I mean during a second it "dies"...
We checked the CDI, and cleaned the whole harness, and sprayed the terminals with Silijet, there's no MIL blinking, we have checked everything...
the thing is that I have to put that bike on sale, since we are buying newer models, but we don't feel comfortable selling the bike with that glitch. imagine the buyer with one wheel in the air and then the bike doing that dying on him... not good...
Well, hope I didn't bore you, and someone may shed some light or ideas, we don't know what else to do....
thanx in advance, and respect for all riders..

Sounds like your speed sensor is shot.

Great!... will check it out! Been busy trying to get a zx-636 w/turbo good enough for the drag races this weekend!
Thanx!

636...turbo? pics?

Ya no kiddin!