1983 XJ750 Maxim Speedometer Reading too Fast

I just got this bike recently, and it was apparent that it had been dropped, but the stock gauges were not on the bike initially, the person I bought it from gave it to me with the bike.

I recently replaced the speedometer cable, and got a new speedometer (in kph), not the right style, to test it. The stock speedometer (in mph) that was on the bike was reading almost double the speed when doing speed tests. The new speedometer was reading correctly (in kph), but I like the style of the old speedometer and tach cluster, and I don’t want to think of speed conversions when I am riding at highway speeds. I took the speedometer apart and checked for damage, but all seemed to be working as intended. Any suggestions?

Tires are stock size, so that’s not an issue.

 

Mine reads about 3mph too fast @40mph.
I have taken mine apart once to get rid of the "scream of death" by cleaning and lubing the gears so if there is a way to take it apart to make an adjustment, I'd like to know.

 

My speedo is off about 3 mph at highway speeds, compared to GPS, so I usually go 60 MPH in a 55 zone and 70 MPH in a 65 zone, if I want to go the legal limit, not with traffic.

 

Yeah, mine is off by about double the speed, not just a small or constant difference, which makes things really hard to track down

.

 

Is that OEM you are talking about there? Any chance someone changed the drive ratio? Stock Yamaha is 2240:60

 

This is the original speedo and tach that was on the bike 40 years ago. How could I tell if the ratio was changed?

 

Update. I attached it to a drill spinning at 2250 RPM and got the 60 mph expected. What does that tell anyone?

 

Wrong drive gear at the wheel???? But then I guess the km/h would have been way off too

 

Which one did you buy or use, did it specify drive ratio?

As expected, so yes the drive gear in the wheel must not be right, but that doesn't seem logical as I haven't found a ratio that would do the doubling

Edit - so one revolution of the wheel should give you approximately 2 3/4 turns of the speedometer cable for Yamaha OEM

 

I bought this one on eBay.

Edit: added part number

eBay number: 383545694170

Yamaha XJ 750 Maxim, 1982-1983, Speedo / Speedometer Cable - XJ750

• sledpartsguy

 

Sorry the question wasn't clear in that previous quote, but I was interested in the speedometer ratio and not the cable. Just wondering if there is a good explanation as to why it was working

Test the turns on the cable per wheel rotation as suggested earlier

 

I would guess someone would have how many little gear teeth are in the OEM and then check what your count on the gear it?

 

the turns on the cable read 2.4-2.5 per rotation of the wheel.
This is the new speedometer that works:
DKMOTORK 0021 KM/H Diameter 2.56 Inches Mechanical Motorcycle Speedometer Dual Odometer Gauge with Led Backlight Neutral Headlight Turn Signal Indicator Stainless 12V Black

on amazon

 

So I found this by searching:

Question:
What is the ratio on this unit I’m looking for 2240:60?
Answer:
Hi, this motorcycle speedometer is 60km/h=1400rpm

DK MOTOR WEBSHOP
SELLER · January 10, 2020

So I believe the 60km/h=1400rpm is the same as 2240:60, which means this should work with stock Yamaha speedo gearing, which you stated it does.

And this also suggests you have stock Yamaha gearing, so if the stock speedometer is not working, then it must be defective.

One other test to do is see how accurate the odometer is by checking its readout with a known distance. If that is pretty much close then more proof the speedometer is defective and typically an intolerable error in speed means replacement

 

I rode a 4.8 mile round trip on the bike, and it read 5.1 miles on the tripometer. It was extremely close.

If the speedo is mechanically broken, how can I fix it?

 

I believe the consensus on this forum would be to just replace it, as a do it yourself calibration usually just results in a broken gauge. The other option of getting it calibrated by a shop might be there, but I can't recall anyone doing that

From another post per hogfiddles:

"The speedy and tach assembly from the 82-83 xj650 maxim is the same for the 83 750 maxim only.... the 82 750 maxim was different"

That said, you could inspect the needle return spring and make sure all looks well. I believe they are somewhat set to where they just bottom on the stop.

https://www.xjbikes.com/forums/threads/speedo-and-tach-dissection-with-pics.15303/

 

Well, thanks. Shame I have to get a new one, but your help was phenomenal

 

Post in the “for sale / wanted” section. My guess is there are a few in the hands of members around here that you could probably get your meat hooks on for less than retail.