07 750 Speedo only reads half

[usmcpi9504]

First, I'm not new to sportbikes. Just sold my 03 GSXR1000 in February. And yes, i searched, no answers. And no, this isn't a speedo healer problem...

Today i went to go look at a couple bikes. 1 guy has both an 05 CBR600 and a 07 GSXR750. So i took the GSXR out for a test ride, noticed speedo said I was going a lot slower than it felt like I was going. Figured I had just been away from my 1000 too long.

So then i took the CBR out and went about the same speeds, although the speedo was right and said i was going 50-60mph. So hoped back on the GSXR, sure enough, it wasnt me, it really was the speedo only reading about half of what I was going. For example, at 7k RPM in third, it said I was going 30mph.

Also, the FI light is on, not sure why. Everything stock except levers, 520 chain (stock geared), etc. He thinks it's because it needs an oil change, but as far as i know, there is no sensor/FI light for that.

Any ideas?

[rp94pj]

The FI light wouldn't be on because it needs an oil change.

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[Ironhead401]

Not sure about the Speedo, maybe somethings up with the Speedo sensor. For the FI light it's not because it needs an oil change. Compete bullshit. Have him pull the code and find out what is wrong.

[usmcpi9504]

yeah, i know its not because it needs an oil change...


When doing the dealer mode jumping, if it has multiple codes, will it just go through all of them on its own or is there something i have to hit to advance to next code?

[TheGeek]

It willl cycle through all the codes automatically and repeat.

Bike might have the final drive ratio changed drastically, or might have a loose speed rotor, or the rotor is damaged. Hard to tell without seeing it.

[le skid]

This is an interesting one. The speedo is a solid state instrument that measures the number of induction pulses from the speed sensor / rotor. IE It either works or it doesn't work. Not sure how it would work but give an incorrect reading.

If it's measuring exactly 1/2 as you say, I'd be curious to pull the front sprocket cover and take a look at the speed sensor rotor. This is just a wild guess but maybe the previous owner ground-off 2 out of 4 of the 'teeth' on the rotor to reduce the miles being recorded on the odometer?

That would explain how it's working but reading 50% of the pulses that should be coming from the speed sensor / rotor at any given speed.

I acknowledge that this is a longshot but it's all I can think of.


this isn't from a gsx-r but it's what I could find with a quick image search. This sits over the front sprocket. See the four 'teeth'? If you ground-off two of them, that would result in what you're reporting.

It would be an easy mod for a sleezebag long distance rider who wants to dishonestly retain more resale value.

[TheGeek]

Ever see a proximity switch (the actual sensor) get flaky and not pickup every pulse? I have. Ever see one of those speed sensor rotors missing an arm? I have. Ever see a loose speed rotor that spins freely on the counter shaft? I have.

[Moto_Joe]

Originally Posted by TheGeek

Ever see a proximity switch (the actual sensor) get flaky and not pickup every pulse? I have. Ever see one of those speed sensor rotors missing an arm? I have. Ever see a loose speed rotor that spins freely on the counter shaft? I have.

Also seen them come loose and hit the sensor giving odd readings

[le skid]

Then the question is: is it reading sporadic / inconsistent or is it steady at 1/2 speed?

[usmcpi9504]

yeah, i read about how that front sprocket nut has the 4 teeth used by the speed sensor. I was also thinking that maybe some of the teeth had broken off. The speedo also reads smoothly, just at the pace of a Civic.