SOHC.co.uk Forums > CB500/550

First Start Highs and Low!

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Neilw:

--- Quote from: McCabe-Thiele (Ted) on October 10, 2026, 02:00:01 PM ---I thought that for a UK bike, the middle position was correct, US  models were one ring position richer.

--- End quote ---

For  my model 1978 CB550 F2 on 069A carbs it's position 2.

I fitted the new plugs and the Bike starts and runs on all 4 cylinders now. I reduced the throttle screw and actually got it ticking over, so now i can go through the tuning process and see if i can get it running smoothly! Quite excited for once !

K2-K6:
If you've got the carb bench sync routine completed to good level, as Bryan's posted routine, then there's no need to change that in "tuning" operation subsequently.

Its easily good enough, when done competently, to give perfect results. Changing it with the use of gauges brings the risk of leading you the wrong way IF there's other elements that affect vacuum accuracy.

Broadly speaking EVERYTHING else in setup needs to be verified and accounted for BEFORE even considering using gauges on it.

It helps with all the other settings to know that the sync is competent in finding other faults.

McCabe-Thiele (Ted):
I do find it confusing that the 500 & 550 are grouped together here.
My 500 needle was in the middle when dismantled so that's how it went back.

K2-K6:

--- Quote from: McCabe-Thiele (Ted) on October 10, 2026, 07:10:31 PM ---I do find it confusing that the 500 & 550 are grouped together here.
My 500 needle was in the middle when dismantled so that's how it went back.

--- End quote ---

It shouldn't make a big and fundamental difference Ted, it's really fine tuning in those steps to set the needle and won't as such give the fault experienced here.

All it does is move the mid range throttle fuelling up or down a little to tweak response or cope with plugs just a little too dark etc.

Clear fundamental issues in mixture will come from wrong spec or worn components to give the bigger steps of error seen so far.

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