Speedometer drive

[JezzaPeach]

My speedo reads 4-5mph or say 10% too high. Does anyone know if there is a drive gear that would fit that would get this more accurate? Thanks in advance.

[Johnwebley]

This is not going to be very helpful,

But all my bikes are similar

Maybe 12% higher than the correct speed

And I fit the correct tyres

Just think of being a money saving device

No nasty speeding fines



Sent from my SM-A546E using Tapatalk

[badger_eng]

If that’s 4-5mph at 30mph, that’s bad.

If it’s 4-5mph at 100mph, that’s not far off being normal. Most speedos read fast. My 2026 Suzuki digital speedo reads about 3mph fast at 75mph. My 2023 Kawasaki was very close at 1mph fast at 70mph. These were measured Vs GOOGLE maps. The only standard in all of the tests was GOOGLE maps.

Have you changed the tyre profile / size to make this suddenly worse or has it been like this all the time?
If the unit is mechanically sound, the magnitude of error should be constant at a constant speed (always 4mph fast at 30mph for example and a larger error at say 70mph), if the error varies at the same constant speed then the speedo drive, cable or speedo itself will likely be the cause.

I haven’t started my Honda resto yet but the two Suzukis (1974 & 1976) I have previously done used the same wheel mounted speedo drive using the same ratio. There was no option to fit another type or a slightly tweaked ratio.

[Bryanj]

There is no option for drives or head, all speedos read high, at one time the legal tolerance was +or- 10% but i believe the - has been removed so you cant argue in court

[McCabe-Thiele (Ted)]

My speedo reads 4-5mph or say 10% too high. Does anyone know if there is a drive gear that would fit that would get this more accurate? Thanks in advance.

How are you measuring the actual speed against the indicated speed?
If its a Satnav - thats pretty standard.
Construction & Use Regulations  at the time allowed for 10% inaccuracy.
How far out is your oddometer, might be worth checking it against fixed road markers for accuracy.

Lastly the damper oil in the speedometer might need fixing, pretty sure there are fixes that clock restorers like KENT400 (Peter Horton) could advise you on.

[JezzaPeach]

Many thanks all. Standard tyres, it sounds like it’s pretty normal. I thought I was getting 50 mpg and on a short test vs Google maps it’s more like 45 mpg. So I’ll do a longer test at steady cruising speed and hopefully that will give an equivalent better consumption nearer say 50mpg (1972 CB500/4) my plugs are quite sooty, partly due to a little oil consumption but I was wondering if it’s rich due to needle/jet wear and if it’s worth, as a test, moving say one needle clip from the current middle notch up one to see if it helps.

[McCabe-Thiele (Ted)]

Google maps for mpg?
The odometer reading is more reliable.
If you are burning oil, weakening the mixture imho is asking for trouble.
Depending on the type of journeys you generally travel a hotter plug might be the answer.
Others here might advise, last thing you want is a holed piston.

I am of the view that higher revs will burn off oil if it's not excessive.
Do you know the cause of the oil burning, is it valve guide/seals or piston wear?
If your oil consumption is based on the recent very hot weather oil burning is not unusual.

It sounds counter intuitive, have you tried adding a small amount of UCL to your petrol?
It's my experience on  car engines that UCL raises compression & makes cold starts easier.
UCL is designed to burn off during combustion without fouling the plugs as it raises the burn temperature.
You don't need to use expensive UCL, cheap Supermarket 2T oil I have found suitable.

[exvalvesetdabbler]

My Prius plugin reads 3-4 mph high against those roadside speed signs.  When I rebuilt the speedo on the CB400 it was 7 mph high at 30, I recalibrated it to 4mph high at 30.

They all read high so you don't sue the manufacturer for getting a ticket.

If your using GPS, need straight and level road.

Regards
Dave

[Oddjob]

The most common cause of oil burning in the 500/550s is worn valve stem seals. They hardly ever get changed due to how much work it involves. Watch for blue smoke on startup and especially on closing the throttle after a high speed blast.

[JezzaPeach]

Many thanks Ted, Dave, Oddjob.
I think the sooting could indeed be valve stem oil seals. I’m not getting and smoke on startup. Or running as far as I know, but I could get someone to follow and observe. Many thanks again.

[McCabe-Thiele (Ted)]

On my cars with poor stem seals or worn  guides there was a simple test I used.

When the engine was hot after a run,switch off, leave the engine for 20-30 minutes to cool a little.
Then start the engine again & blip the throttle. A puff of blue smoke indicated there was a problem.

[Skoti]

Many thanks all. Standard tyres, it sounds like it’s pretty normal. I thought I was getting 50 mpg and on a short test vs Google maps it’s more like 45 mpg. So I’ll do a longer test at steady cruising speed and hopefully that will give an equivalent better consumption nearer say 50mpg (1972 CB500/4) my plugs are quite sooty, partly due to a little oil consumption but I was wondering if it’s rich due to needle/jet wear and if it’s worth, as a test, moving say one needle clip from the current middle notch up one to see if it helps.

For me sooty plugs and bad fuel consumption usually means worn needle jets, they last around 15,000 miles on my CB750F1.
But they always wear oval, so lowering the needles is not the best solution.


A new set always brings better fuel consumption and performance with a punch.


Genuine Honda brass ware is best

https://www.cmsnl.com/en-gb/honda-cb500k1-four-england_model14660/needle-set-jet_16012323004/


Pattern also available

https://www.davidsilverspares.co.uk/parts/by-part-number/partnumber_16012323004P


Good luck


 

[JezzaPeach]

Many thanks Skoti 👍