How do I change my speedometer system to read in MPH?

[88jog]

So, a little background first.

I have a 1988 Yamaha Jog CG50.  I got it in 1999 and used it in college.  It's a US model so the speedometer display is calibrated in MPH.  About a year later I let someone drive it and they managed to crash, so I rebuilt it.  My memory is a little hazy, but I replaced the speedo cable and/or replaced the front wheel with items purchased on ebay and scrap yards.

I recently got the urge to get it running after about 10 years of storage, and managed to do so pretty easily.  But I realized that the speedometer needle is actually pointing to kph on the mph scale.  In other words, if I'm driving at 20 mph the speedo needle would be pointing to 32 mph which is how fast I'm actually going in kph.  If I move at top speed (variator shim removed, 43 mph by GPS) the needle is bottomed out at the bottom of the speedo.

This is annoying, and I'd like to fix it the easiest way possible.  It also adds extra miles to the odometer every time I drive it.

Can someone tell me how I screwed up when I rebuilt the scoot, and what the cheapest/easiest way to fix the issue would be?

I'm assuming something is messed up with the speedo gearing in the wheel hub.  Maybe I put a kph wheel on a mph scoot if I replaced the wheel?  I dont think I replaced the wheel though, it appears to still have the original white rims on it which I repainted flat black (looks badass).  I know I bought a pair of purple wheels from a 90's model CY50 Jog on ebay, which I only used for the tires, as the purple wheels are still in the shed.  Maybe I moved the speedo gear from the purple wheels to the original wheels?  Would it be possible to mess this up with just the speedo cable which I think I purchased at a scooter salvage yard or possibly ebay as well?

Also, I'm in the process of tuning the carb for a pod filter, and have to increase the main jet size.  I managed to find a 77.5 locally, but I don't know what the factory main jet is for a starting point as it is unmarked.  Anyone know what the factory jet size is?

Thanks, and if possible part numbers for the speedo fix would be useful.

[jackrides]

Sometimes the easy way is best. Stick small printed labels on the speedo with the mph numbers on them.

[benji]

I would search for a stock wheel speedo cable thingy. Yours might be defective or for the wrong bike.

[ryan_ott]

If you swapped the brake drum hubs around they hold the speedo drive gears and you could of changed to one with more gears. It looks like yours is supposed to be a 14 tooth.

www.partzilla.com/catalog/yamaha/scooter/1988/cg50eu/front-wheel

[88jog]

Its got to be something like this.

Although I havent actually tested to see if the odometer is accurate. If it is, it means the speedo is actually faulty. That will be next on the list.

Thinking about it I cant imagine that they have different gearings for kph and mph. They would just change the display on the speedo.  But then they would need different gears inside the speedo to keep the odometer accurate.  So they either do it at the hub or in the speedo but not both.

[ThaiGyro]

Dec 5, 2017 0:31:33 GMT -5 jackrides said:

Sometimes the easy way is best. Stick small printed labels on the speedo with the mph numbers on them.

I'm with jackrides:  Actually, I don't GAS about speed, unless for fun and tuning data.  Do as jack says...a little pin stripe tape makes it simple!

Basic assumptions work up to near 60 mph.  Use 16 kph for each 10 miles per hour. (at 60 it is actually near 17 kph, but again, who cares?)

Most American cars have both scales, so you can look for yourself.  I would never spend a dime on speed indication, unless you are concerned with the Po-Po pulling you over for doing 40 in a 25.  Shame, shame, shame!

Trail Tech make the alternative easy. Spend 135 to 165 dollars and get a thick-ass cable that is ugly, but reliable. Koso has similar, but has a GPS transmitter option, which works quite well, or a KOSO speedo gear to match your scoot. IMO, they make Trail Tech look dumb, though the TT dash is nicer.  Look at Stage 6...Trail tech in orange. Huge bucks for no valuable return.

[mpfine]

You may also consider the front tire size. My Jog was 11 mph optimistic until I changed the front tire from an 80/90-10 to a 3.50-10. Now the spedo is about 1 mph off. And, looks like the rest of the spedo effecting parts are stock on my scoot.

[moofus02]

I took a us zuma with a 40mph speedo and put a bws100 speedo on it that reads to 140kph on the zuma/bws the difference is the speedo no idea in the jog

[eclark5483]

Who looks at the speedometer? I just use a GPS APP.

[ThaiGyro]

Hahahaaaa! My opinion as well. My Gyro cannot take a squat without a tail wind...when I hit 49mph? Celebration! Everyday indication? RPM, temperature...and fuel level.

[pitobread]

s.click.aliexpress.com/e/oEgNSU0s

I have one of these, waterproof, GPS, Backlight. Bicycle Computer

Only cable I have running to it is a 12v to 5v usb power plug.  s.click.aliexpress.com/e/C9fVzy4s

No cords, cables or other fluff. Can also upload rides from it to get maps.