High CO Emission

[MMM1960]

I took my Mini for the roadworthiness inspection here in Sweden and it had two issues - brakes uneven stopping on the rear and high CO. I can easily sort the brakes but what are the main things to check for high CO? Mixture? The level was 9.2 whereas the limit is 4.5 for cars of this age.

I’m changing the oil and filter this week but I doubt that would get the reading down much? The air filter is as new.

I’ve heard people in Sweden mention putting k-sprit in the tank before inspection to bring the reading down but I would rather sort the problem than mask it.

[MiNiKiN]

Twin carb or single carb? What carburettor?

generally you would adjust the jet adjusting nut, which is visible beneath of the carb.
Turning the nut upwards (tightening) will weaken the mixture - turning it downwards (loosening) will make the mixture richer.
You can buy an SU jet adjusting spanner to make this adjustment easier.
The starting position for adjustment (If start from scratch) loosening it by 12 flats of the nut (I think that's 2 full turns) from the fully tightened position. Before you start, adjusting --> count the number of flats from its current position to fully tightened, so you know where it how far it was off.

Also check damper oil level first and if there is any leaks (e.g. from the throttle valve shaft and bore)

Look for the SU tuning manual for more info - available here: http://mk1-performance-conversions.co.uk/hs_tuning.pdf

[Lakeland997]

High CO means incomplete combustion.
There's no one fix for this but the most likely causes are too much fuel or poor ignition.
Can you tell us more about your Mini? SPi? MPi? carburettor(s)? Points or electronic ignition?

Andy

[iain1967s]

How long since the carb was rebuilt - could be oval wear in the jet tube causing excessive fueling. Rebuild kits for SU are readily available with butterfly, new needles and tube.

Yours being a 1960 car, it may have the older style vacuum advance copper pipe with vapor trap near the carb end. Consider fitting a more reliable modern vacuum advance diaphragm with straight-through plastic pipe, at least to get it through the test.

[MMM1960]

Thanks for all of the information and suggestions.

I only recently purchased the car so am not certain when the carb was last rebuilt.

From the engine rebuild sheet it seems the single carb is HS2 1.25” with an EB needle but this may have been changed as two other owners had the car since then and the sheet suggests an M needle might be optimal.

Tonight I found that the choke is not closing off properly near the carb despite being in as far as it will go (although not all the way in) inside the car. I guess the choke sticking on would contribute to the high CO level.