Just bought an F3....some help...
 

Hello, I am new to this forum first off, and I really look forward to all the information I can find here. I recently purchased a 1997 CBR 600 F3, and everything is really sound with the bike except that I am missing the rear seat "cowl" I do beleive it is called. But more to the problem at hand.

While driving back to school today, I finally came to the conclusion that the speedometer is wrong. When the speedo reported 75-80 I was really only going about 60. The ratio that the speedoo is wrong seems to change depending on how fast I am going. It would be one thing to just memorize new numbers to look at for my speedometer, yet I know that will just not work forever. I was not told of this problem when I got the bike, so I am really hopeing this will be a quick/not cost much money fix. Does anyone have any suggestions on a place to start to troubleshoot this problem? The bike has all stock parts, or so I was told, and the gauges have not been changed.

Any help would be really awsome! Thanks guys.

Bikes are notorious for having inaccurate speedometers. However, that's quite a bit. An example is if my speedometer reads 75 mph, I'm actually going 68 based on a GPS on the bike. I suspect that someone has changed the sprockets on your bike, which is a common thing. Your bike came stock with 15/43 sprockets, meaning 15 teeth on the front sprocket and 43 teeth on the rear sprocket. It's easy to count the teeth on the rear sprocket (or look for a number stamped on the sprocket). The front one you'll have to remove the sprocket cover which is held on with 2 8mm bolts.

Give them a count and let us know what you find.

Alright so I checked the back sprocket, and it has the correct amount of teeth. I don't have the necessary tools right now to check the front one though quite yet.

Alright so a bit a reviving an old post instead of starting a new one. I finaly got around to checking the sprockets on my bike. The back one is fine, 43 teeth, yet the front.....14...not the 15 that is stock. Is this enough to throw my speedometer off so much? I am beginning to believe that this bike was once it much worse condition, or the guy thought that one less tooth would make it perform better.

I don't know the specifics about changing sprockets or what the different sizes are, but I know mine is less than stock and this leaves me with a difference is speeds reported on my bike, also I believe that it throws off the mileage as well it is in-fact has less then 22k miles on the bike.

If you could help me with some input on the sprockets and ways I could correct this it would be great. Is there anything I should be checking out inside the actual gauge cluster?? Could there be something wrong in that?

dropping one tooth in the front allows the bike to have better low end acceleration. this, (debatable) sacrifices top end. When doing so, it can make your speedo 10%-15% off... mine was like yours when I dropped 1 on the front. now if your speedo is already off 5-10% from time/miles/etc (age)... then you could be looking at as much as 25% of incorrect reading.

You can fix this by either returning your front sprocket to 15,
or buying a speedohealer
http://www.healtech-electronics.com/
the latter will adjust your speed to read correctly (since it is not cable driven, but digital instead), and runs about 100.00 on ebay.

which would be less expensive? The new sprocket or the speedohealer, also is there a way to check to to make sure which is the most probable culprit?

The quick fix is get the speedo healer. They are about 110.00 and take about 1 hour for most people to install. Even if you change your sprocket back to the stock size you will still be about 8-10 percent off on the speedo. If you replace the sprockets you should do the pair and get a new chain, looking at 150-200 dollars. You will lose out on some of the low end acceleration.
Tom

Replacing the front sprocket, it will still be off a bit, as stock speedometers are off around 5.5%. Speedohealer is the only way to get it accurate.

A -1 on the front makes it around 14.3% off with a medium wear tire. That equals about what you're getting now, reading 75, doing 63. With excessive tire wear, it gets worse.

well that sucks.....looks like I might have to wait around on this one so I can get some money set aside for the part to actually fix it right and get the speed-o-healer

5% off is in the US DOT's tolerances. If you go back to stock sprockets we're talking the speedo reading 95-105 if you're doing 100 mph. Seriously, most cops don't even bother with +5 over the limit because of it.

I swear people with OCD should never ride motorcycles. It'd murder them :p