Emissions and a daft MOT fail!

Z

zebedee37

New Member
My 1972 2000TC failed my countries equivelent of the MOT today

1. Because the rubber was missing on an over-rider!! (Passed the previous 2 years with rubber missing)

2. More seriously on emissions. The CO² has to be below 4.5% and I am struggling to achieve that (in the past it has dropped below that for a few seconds and the tester has let it through, this time a new "jobsworth" on duty.

So what can I do to get my CO² below 4.5% for the period of the test? Im going to take out the airfilters in the car park and put them back after! Any addatives I can use etc etc?

I shall be playing at the weekend with my gunsons gas tester and trying to coax a lower constant reading!
 
Before you start messing with the carbs, make sure the ignition system is up to spec, new plugs and points properly setup can make a big diference to emissions. Then I guess you start winding the jets in, a colourtune (preferably 2) can help on the TC to prevent getting the mixture unbalanced. I saw a TC head once that had 1/4 inch of carbon build up in the inlet manifold but only for the front two cylinders, the runners for the rear 2 were clean !!
 
Forgot to mention, our MOT can be pretty flakey too, I had 3 tests on my old convertible before somebody decided the front wings weren't secure, nothing had changed, just nobody cared before !

I also took my Chevette for a test once and it failed on something silly, I wasn't happy with the garage so I took it somewhere else (back when tests were £10), they found a 6 inch hole in the chassis which the other garage completely missed !
 
Oh Dear! (i'm sure that's what you will have said when he failed it!) I'm with Richard on this. It's well worth spending a full weekend getting everything properly fettled. There have been a few posts on both the hazards of the ignition system and the wrinkles to setting up twin carbs. Only when you've got it properly set up is it worth starting the hunt for "dodges" to get it through the test and to be put right after.

I'm not too familiar with the terminology in this area, but don't you mean CO rather than CO2? Either way you're looking for anything that will give you more complete combustion whether at the expense of the engine or not! So missing out the air filters would be good. So would marginally weakening the mixture by turning back both carbs by an equal amount from the ideal setting you've just painstakingly achieved. Expect pinking and running on for the time you have to tolerate this! If neither of these are sufficient try marginally advancing the ignition (more time after the spark before the exhaust valves open) again at the expense of pinking and running on!

Hope that helps

Chris
 
chrisyork said:
If neither of these are sufficient try marginally advancing the ignition (more time after the spark before the exhaust valves open) again at the expense of pinking and running on!

Chris
Click to expand...
Actually if you advance the ignition you 're going for sure to have problems with high hydrocarbons emissions at idle. So, it is not a good thing.
But you don't have to worry too much. If you set it up properly and the ignition and carbs are in a reasonable state, even a worn out engine like mine with tight valve clearances went through the test last year. The limits were 4,5% CO and 800 ppm for HC.
Both at idle and 2500 rpm.

Good luck with this...

Demetris
 
Usually on these if you weaken them off too much you get popping back through the carbs, gives you a nasty shock the first time it happens with your head under the bonnet !
Even on my totally knackered TC carbs I could get it through no problem. Although quite often I managed to convince the tester that it was exempt ! :D
 
That is a good point Richard made.

Not all P6 in the UK need to pass an emissions test. most will be just the smoke check but if like me you own a late car then you get checked but only to the standards that were current on the date of manufacture. Is the tester using the correct standards for your test?

I would invest in a Gunson colour tune and check the mixture and try the air filter trick if the mixture is weak. There is also products you put into the petrol that claim to reduce carbon build up and decoke the head.

Colin
 
Alas yes - here cars have to pass minimum of 4.5% CO if they are old. there is an option to have a "classic car" registration without pollution tests - but the limitations are great! (so much so that you may as well not have the car!)
 
Well done that man! What dodges/work did you do to get it through and has it improved the car as a result?

Chris
 
I've only ever bodged one car through the emissions test and that was my single point injection 820, which requires a unique plug in test unit to set the base mixture (I now have one of these units). I had tried loads of garages to get it done but nobody had the right box. So I just pulled one of the vac lines off round the back of the inlet manifold, this obviously weekened the mixture and the ECU compensated for the increased idle speed by closing the throttle a little, the car passed.
 
webmaster said:
I've only ever bodged one car through the emissions test
Click to expand...
I have to do it every year in the Austin. Because of the fast road camshaft the HC at idle are somewhat marginal. So for good measure i open up the valve clearances a little, retard the ignition, and raise the idle speed. It works miracles!
 
I have to confess to not being the worlds greates mechanic! though happy with a manual to get my hands dirty!!.Having experimented at home adjusting a screw to the right of each carb the same amount and getting the emissions low borderline (but the car cutting out totally on touching the accelerator. I arrived at the station, adjusted, passed and adjusted back!

Is there a simple book on how to tune TC carbs?
 
What alot of people do is adjust the fast idle screws opposed the mixture screws. this can really make the car run badly it can especially knock the balance out. It sounds like you may have made this mistake.

If you stand at the side of the car and look at the carbs. You will notice that the cable operates the front carb and there is a connecting rod that operates the rear carb. If you have a manual the look at the diagrams and get familiar with the parts of the carb. the little scews alter when they start to open up when the pedal is operated. If you were to take the filter housing off and get some one to press the pedal whilst you put the heel of your hand over the holes you will feel that one sucks harder than the other, both should actually feel the same.

Does you car have the HIF or the HS type carbs? I think it is the HS one with the float to the side and the mixture below.

Do you have a manual for the car? if you need I can scan a section for you.

Colin
 
Thanks

I do have a manual which I will be investigating when tis found in whichever box it is hiding in!!. I have also just found my carb balancer (never used and bought years ago!!) fortunately has instructions with it!
 
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