MOT Fail on Emissions, Re-test Tomorrow. Help!

[jayvoa]

The Capri went in for the dreaded test today and failed on emissions (one or two advisories but everything else was ok). I was told the law on emissions got stricter this year... The mechanic said he would have tweaked the fuel mixture himself to get it through, but doesn't know his way around an old Pinto engine and didn't want to mess it up. He's going to pick the car up from my work tomorrow for a re-test and wants me to show him how to adjust the carb to lower the emissions.

I'm wondering if tweaking the fuel mixture screw would be enough to lower the emissions? What can I do with basic tools myself to try and lower these damned emissions? I'm thinking of tweaking it a little tonight to get a bit of a head start but wanted to ask here before I do anything. Oh and I only have basic tools as I'm not at home. With no MOT and tax due tomorrow I'm staying close to work to minimise my time on the road.

Any help is massively appreciated!

[vaughant]

I would do just as he's offered really fella,just show him where the adjustment screw is and get him to sort it out in the garage,he'll have the proper test equipment to get it bang on.
Otherwise just check for exhaust/inlet leaks,split vacuum hoses etc which fixing now will save you a few ££££ in the future.

[welshpug]

emissions regs have not changed for pre cat cars for a very long time.

[jayvoa]

Cheers vaughant. I'll take a look at whether there's any leaks. I try to check fairly often for things like that so fingers crossed it's not that, but I'll take a good look.

Just a thought... I'm reading about adjusting the carb and one guide says to turn the idle screw until the engine is running as fast as possible, then turning the fuel mixture screw right down, then turning the idle screw back to the correct revs. Another guide states what seems like the opposite, which is to turn the mixture screw all the way so that the engine is running fast as possible, then adjust the idle screw to bring the revs back down.

Which of these is likely to work best? Or would either method achieve the same thing? I'm just wondering if it's worth me telling the mechanic about either of these methods as he doesn't know his old motors.

[Deleted]

If it is running ok at the moment then make a record of the settings before you start (screw the mixture screw in gently and count the turns until it is fully in then back it out again). That way you can always reset it after the mot. I've forgotten to do this more than once!

To be honest if the guy is happy to adjust it for you whilst he is measuring it then just hook it up and adjust the mix until it passes. You can do it by ear but if it is being monitored its a lot easier.

[jayvoa]

Cheers for the advice guys.

welshpug: I've had a look on the trusty gov.uk website and found a document that gives details on emissions test. Cars from 1/8/75 and before 1/8/86 have a max value of 4.5% vol CO and 0.12% vol (1200ppm) HC. I'll print this off and run it by the mechanic to make sure all's ok.

chip: Thanks for the heads up! It's running well at the moment so I'll make a note and sure to re-adjust the carb after the test.

[ben711200]

Just point at the mixture screw and ask him to adjust it until it just passes. I wouldn't worry about trying to follow any tune up guides- that will just lose you the reliable base setting you have now and could make it better or worse with no way of you knowing what it's doing.

[ChasR]

Which part of the emmisions did it fail on?

On one of my cars despite the idle mixture screws being set as low as they could go (the car would run with them lower, but it would cut out when the revs fell down) the emmisions could not be passed (fortunately it was a pre -75 car). In the end it turned out to be HT issue (curse word leads despite being relatively new (read less than 18 months old and 5k on them) and overadvanced ignition timing (the crank pulley had slipped out a few degrees). FWIW that passed the lambda and HC part, but not the CO (it was about 6% from memory).

[misterbob]

As Chas has touched on, you really need to ensure your ignition system is in good shape first.
Leads in good condition? Plugs in good shape, and gapped correctly? Most importantly, is the ignition timing correctly set?

Only once the ignition system is properly set can you really stand a chance of getting the carb set up properly.
ideally with a CO meter, but a really great budget alternative is a Gunson Colourtune plug. Lets you set the mixture based purely on the colour of the flame front.

Good luck with the MOT!

[jayvoa]

Cheers for the advice guys. Leads are all new (power spark brand if I remember?) as well as the spark plugs. It was the CO it failed on too. As far as I'm aware the timing is correct, so I'm hoping it's just running too rich... If I manage to get through this test then I think I'll have to invest in a colour tune kit. Heard lots of good things about them and could have done with it before this test!

[bortaf]

Just keep in mind the so called "mixture" screw only alters the mixture on idle and not over the entier rev range

[jayvoa]

Ah true. Pre-86 motors only need to be tested at idle don't they?

The mechanic just picked the car up from my work and I've shown him what's what on the carb, so hopefully with a little adjusting it should pass!

[jayvoa]

He just dropped it off at my work... It passed!! Another year of glorious retro motoring! All he had to do was turn in the mixture screw until it went from 9% CO to almost 0%. Well chuffed!

[Deleted]

... It passed!!

Great news!

[Deleted]

Next year find a tester that knows the rules, they have not changed for pre 1986 cars and as for ChasR'S car failing, pre 75 don't require an emissions test they only get a visual smoke check.