How to reduce co emmissions for mot

Post by **toshT25** » 09 Sep 2008, 20:19

Ok, just had a mot done and it failed on co emmission, recorded 7.05% (4.5 max) Before I took it in I changed the spark plugs and fuel filter (near carb) oil was changed 500 miles ago but I added another litre as was only half full and looked a bit black

They're going to take a look at it, to get it through (probably carb tune) but is there anything else I can do before taking it back as its £50+vat per hour

I'm going to change the air filter (even though it looks clean) and change the oil again.

btw I took it for a 70mph run for 20mins right before it was tested

hc level was 479ppm

its a1.9dg petrol waterboxer with solex carb

cheers

Post by **kevtherev** » 09 Sep 2008, 20:31

is a solex 34 pict 3?

turn idle mixture screw in fully, then out 2 1/2 turns. set idle at 800-900rpm using the override screw.

Post by **toshT25** » 09 Sep 2008, 21:08

Thanks for the reply

Looks like a solex 34 pict 5 if they make one, haven't got the van here but a pic I took earlier looks like a digit 5

[IMG:150:128]http://img359.imageshack.us/img359/5341/solexxx5.th.jpg[/img]

if it is a 5 is it the same procedure?

Post by **kevtherev** » 09 Sep 2008, 21:48

ignore my last post this is far more instructive

http://www.vw-resource.com/34pict3.html

not sure about your question ... but if you can find these adjustment points on yours.. it may be the same

[img

1234]http://www.vw-resource.com/images/34car ... d_view.jpg[/img]

1 Fillister head screw and lock washer (upper body (5)

23 Accelerator pump diaphram spring

2 Spring washer

24* Accelerator pump diaphram

3 Carburetor upper part

25 Cotter pin

4*Float valve washer

26 1-mm (.040 in.) thick washer (2)

5*Float valve

27 Connecting rod spring

6*Gasket, carburetor body

28 Connecting link

7*Float pin retainer

29 Adjustable bell crank

8 Float and pivot pin

30 Circlip

9 Air correction jet with emulsion tube

31 Adjusting segment

10 Carburetor body

32 Accelerator pump cover

11 Pilot air drilling

34 Screw

12 Auxiliary air drilling

34 Pilot jet

13 Bypass screw

35 Vacuum diaphram cover

14 Main jet cover plug

36 Oval head screw (3)

15*Main jet cover plug seal

37 Vacuum diaphragm spring

16 Electromagnetic cutoff valve

38* Vacuum diaphram

17 Main jet

39 Plastic cap

18 Volume control screw and O-ring

40 Choke heating element

19 Fast idle lever

41 Cover retaining ring

20 Throttle valve lever

42 Retaining ring spacer (3)

21 Throttle return spring

43 Small fillister head screw (3)

22 Accelerator pump injector

Post by **HarryMann** » 09 Sep 2008, 22:11

Brickyards info on emissions

Post by **Red Westie** » 09 Sep 2008, 23:12

The figure they have given you appears to be the idle CO which can be easily tweaked to drop the reading below the 4.5% threshold. Note the starting point on the CO adjusting screw, warm up the engine, turn the CO screw in very slowly until the engine starts to miss/slow and then screw out approx 1/8-1/4 turn. Hopefully the screw will be in further than it was when you started and therefore a leaner idle CO reading will be attained.
I know that this is not an exacting science but unless you have a proper gas analizer it will be close enough.
What people fail to realise is that this adjustment only effects the idle CO, as soon as the engine revs come off idle other jets take over so in the overall run of things idle CO is a bit of a joke! it doesn't really give the overall emmisions picture (how much pollutant the engine is giving out when properly running) unless of course you intend to just sit there all day sat on the drive with the engine idling.
I take it that it past the other speed emmisions tests? but just failed at idle? as I say a quick tweak on the mixture screw should see it pass and to be honest...it is something the mechanic could have done in less than 5 minutes. (or is it that he didn't have a clue about carburretors?)
Martin (EX MOT tester)

Post by **toshT25** » 09 Sep 2008, 23:26

Thanks for the info guys, 1000% better than a haynes book

now I can see what the problem might be, so now I have to decide whether to let the mot mechanics try to tune it or take it to a mechanic who specializes in these old carbs

thanks again

Post by **toshT25** » 09 Sep 2008, 23:36

E D I T:re last post thanks, something more to ponder, might give that ago

these were the results,

1. idle speed = pass
2. smoke level = pass
3. co level = fail 7.05% max 4.50%
4. hc level = pass 479ppm max1200

Post by **HarryMann** » 10 Sep 2008, 00:08

I would! As Red says, idle CO is really a bit of a joke, unless you sit in traffic jams all day, if it won't run wound down to 3~4 % then there's something wrong

Theres a few other topics knocking a round at the moment on those carbs..

Post by **toshT25** » 10 Sep 2008, 00:22

I'm confused now, does the tweaking with the CO adjusting screw sort out the prob (lower it to under 4.5%) apply to 1. idle speed or 3. co level

it is late

Post by **HarryMann** » 10 Sep 2008, 00:44

1 Idle speed is the rpm at idle...
3 CO is what we're trying to correct

But if it won't run at the correct idle speed when idle mixture is weakened without hunting (trying to find a steady speed, e.g. speeding up and slowing down- an indication of weakness in itself), then there's prob. something else wrong (air leak, poor compressions, exhaust leak etc.)

Post by **toshT25** » 10 Sep 2008, 00:51

thanks, i'll give it ago tomorrow today and see if it hunts

cheers

Post by **Rozzo** » 11 Sep 2008, 18:58

take the air filter out

oh and they are allowed to increase the idle speed on older stuff but most testers don't seem to know this

Post by **jamesc76** » 11 Sep 2008, 19:07

When i was Mot stuff older vehicles if cannot pass the emmisions test at idle then test can be carried out at 2000 to 2500 that might help?

Post by **Red Westie** » 11 Sep 2008, 22:58

Somewhere around 1/2 turn in on the small mixture screw...but as I said.. get it up to temp...get the idle about right on the air by-pass (the larger screw...turn the mixture screw in slowly (needs to be quiet so you can hear the changing pitch of the engine) you will get to a point where the engine starts missing a beat (it is getting lean) at this point reverse the screw motion until the tick over runs smooth again (1/8th to 1/4 turn out) bobs a fish!
If you have taken note of the mixture screws original position it should be in further after adjustment.
My guessing is NOW....your idle CO is 2-3% job done.
Looking at your figures there isn't anything else wrong...just the idle CO so you haven't got any major problems (worn rings etc)
Martin