SOHC.co.uk Forums > CB500/550

Speedometer drive

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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.

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