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MG Midget and Sprite Technical - CO Levels ?

I have a gunson Gastester,it is a good bit of kit but its not a lot of good if I cannot find out what the levels should be, for my 1973 1275.
Did a test this morning, and after the required calibration period at 2.00, and with the engine at normal temperature, I got a reading of between 3.4, and 4.00.
I think this is about right, but without knowing what the reading should be, I cant tell.
Anybody know what the reading should be,?.

Thanks Dave
Dave Barrow

Sounds in the right ball park.

I don't know what the MOT requirement is, but does this help for general info?

Malcolm Le Chevalier

Make sure you put the tester as far away from the exhaust pipe as possiable
Prop and the Blackhole Midget

That's not very easy Prop, as you are not supposed to move the tester after its eight minute calibration period, you have to place the probe in the exhaust without moving anything. So you are limited by the length of tubing.
The only thing you can do is place it at the side.

Dave Barrow

For a simple engine like this with carbs I would be happy with anything under 4% CO. There's no requirement for CO testing for vehicles manufactured before 1st August 1975, but after that date the max is 4.5% up to 31st July 1986 when stricter limits apply.
Mike Howlett

Yeah, put the tester as far away as possible. In the garden would be ideal. Makes for a much better CO reading :-)
Malcolm Le Chevalier

It's as Mike put you don't need it for MoT but for yourself the information can be found in the Driver's Handbook (the booklet that came with the car when it was new) As I happen to have a copy I looked it up for you and it shows -

"Exhaust gas content (carbon monoxide) at idle 3 to 4.5%".

Ref; 0057 -

This of course relates to the time and when the car was new so is a general figure for you, yours might be within, better or worse.

IIRC (and I might be wrong about this) the MoT tester does a visual check for excessive smoke(?), you can check here if you're interested -
Nigel Atkins

Thanks all,I use the tester to help in tuning the carbs, not for the MOT, so looks like I have got them about right.
The reading was 5-6 when I first tried it, so weakened the mixture a bit which brought it down.

Dave Barrow

We had one of those on test years ago and were comparing it to our 2000 Camic infra red CO/HC tester. The Gunsons was nowhere near and after a power run sampling it belched out smoke and died, with the needle twitching in a rather sad dying animal way :(
You may be better off just doing the piston lift test or just let it come back to idle. Too weak and it drops below idle then comes back up. Too rich and it drops to idle then slowly loses rpm. We tend to set the carbs so we get no difference in rpm when we lift the pistons a little.
Peter Burgess Tuning

I'm with Peter. I have a Gunson mix tester thing - the one where you stick it in the plughole and view the colour of the flame. Total waste of money. I reverted to the SU manual instead and some previous knowledge of carb setting from motorbikes. Nothing beats skill and experience...

This thread was discussed between 01/09/2016 and 02/09/2016

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