How to bring down CO emissions a percent?

[soldave]

One of my MOT failures this year was CO emissions, which I've not had before. Whilst 4.5% is permitted, I had a value of 5.51%. A little strange as nothing's really been done on that side apart from a tune last summer, but that's besides the point. The main point is that I need to bring down CO levels by 1% and I'm not sure how best to do it. Is it a case of pulling out the Colourtune and making sure everything looks good in terms of spark colour in the cylinders, or is there a better method?

Any advice on this would be greatly appreciated.

[Clive59]

Can only suggest going through the carb balancing, and then see. I went through the procedure, and had a go with colourtune but couldn't improve by using it. See if this doc(from Tim Engel) gives some ideas. btw, my idle CO was around 1.2% I seem to recall, but also check and recheck float levels, they make a huge difference on drivability. And check jets?

Balancing Dellorto.docx

[pbharcourt]

Take the air filter out for mot?

[910Esprit]

All your mixture screws 1/2 turn clockwise would probably be getting close, as long as it doesn't start spitting back or 'coughing' in the carbs.   Also maybe increase tickover by a couple of 100 revs.   The  only risk of weakening the mixture is that the NOX may start to rise.  If it goes out of the allowable limits you've gone too far

[soldave]

Might try all of those. HC were only 329 (limit of 1200) so hot plenty wiggle room on that side of things.

Thanks for the advice 👍

[910Esprit]

Yes, I meant HC! - Good luck

[jonwat]

9 hours ago, soldave said:

 Is it a case of pulling out the Colourtune and making sure everything looks good in terms of spark colour in the cylinders, or is there a better method?

Yes, colortune always worked well for me, of course you need to make sure the carbs are balanced as well. I always used a monometer. 

[soldave]

Well, many thanks to a very generous fellow, I have been able to do some exhaust emissions testing after work today. According to the meter I started at 5.6% CO which is pretty close to what the MOT centre had. Went through the carb balancing process and once done tested again. 3% was the final figure which I'm pretty happy with. We'll find out on Saturday what the official figures say but, touch wood, I should be in a good place.

[soldave]

Success. Re-did MOT today and got CO emissions of 2.68% and HC of 685ppm which is much better, and also within the Lotus factory specs for CO emissions. All good and problem solved