I have put this topic here for my carb turbo although its an early Stevens model. When I rebuilt my engine a few years ago, I balanced the carbs using the correct manometer and recheck from time to time and all seems correct. However the mixture is a bit of guesswork. I tried using the colortune but frankly couldnt really  get on with it so used the factory initial setting of 6 half turns out from closed. Took it to the MOT and emissions seemed fine and have passed each year since with the tester always saying mixture seems fine so dont fiddle. However readings over the 3 MOTs seem a bit erratic.

 

They are as follows:

 

2012 -  CO level - 2.93%

            HC level - 141ppm

 

2013 - CO level - 0.20%

           HC level - 678ppm

 

2014 - CO level - 2.61%

           HC level - 104ppm

 

According to their gas analyser CO should be 3.5% max and HC level 1200 ppm max

 

I appreciate a lot of factors come into play which can affect readings but Is there anything I can interpret from this data apart from its within range. Does it suggest lean or rich running. Also, be interesting to compare it with reading other have for their cars.  

The lambda reading is a good indicator of rich or lean running. High CO would indicate its running rich. HC is a measure of how well the fuel oxygen mixture is burning.

 

You can't really infer anything from those readings, as you don't have the context in which they are taken.  When the emissions fall within tolerance, the tester hits the button and the report churns out.  Any number of factors can affect it - engine temperature, ambient temperature, atmospheric pressure, rpm - the list is long.

 

The MoT emission test is not particularly accurate and only serves to give a tick in the box at that point in time.  To improve accuracy to any useful level you need to throw cash at a tuning specialist.

My car failed its MOT in CO2 emmisions yesterday.  I don't have the paperwork to hand but it was nearly double the pass figure.  It was OK on HC and the other two categories.

mine where the same so we had to "adjust" them to pass, now i need to reset them unfortunately,there is no carb blokes around weymouth    i know people talk regarding colour tune ,seems it might be hard to get a good look at the thing with the engine laid over as it is ,please correct me !!!

ColourTune thingies come with an extension tube so that you can see what's going on. Sadly, I have never managed to get mine to screw into the plug threads....always seems to be going in crossthreaded when I put the thing in with my fingers; never got to the point of using the plug spanner.

I used my colourtune for the first time last weekend, and like John I also had problems with crossthreading (although the end nearest the back of the car went in OK.  I was still able to use it though even though it was barely screwed in to the other 3.

 

Cylinders 1 & 4 were too high, so I have lowered them down so they now show blue.  Interestingly I wound the idles screws back before doing this and they were 8.5 turns out from seating, and I have wound a & 4 back 2-3 turns which does take it to the 6.5 base level.

 

Ticking over the same but I have some popping now...

The carbs Must be balanced at the same time as setting the mixture.

ie: set the base mixture to 3 1/2 turns on each carb

Balance the carbs to set the vacuum:-

fully close all balancing screw, then adjust the throttle coupling between the carbs if necessary to get the lowest columns off each carb reading within 3mm, then adjust the higher of the readings to the lower by opening the balance screws on the relevant pots

Then you can set the mixtures , by moving all 4 screws by the same amount

Then recheck the balance and set the mixtures again

I am reviving this thread as I am still struggling, and the car failed its MOT again on emissions.

 

As per Dodgys advice above I invested in a balancer and balanced them up.  The slave side needed dropping down slightly, and the popping I referred to in post 7 went.  She was actually running pretty well.

 

The figures on August 15th when it failed where:

 

CO2 - 7.689% (pass rate 4.5%)

HC - 625ppm (pass rate 1200)

 

Todays figures following my adjustments were:

 

CO2 - 8.73 (so even worse)

HC - 1823 (way way worse)

 

So I have made it worse.  You can see now why I hate doing stuff I have never done before because it never goes to right (and that's not me being negative, its a fact!!!)

 

I keep being told there may be a build up in the engine which is giving me a high figure, I assume the only way I can clear this would be by using some petrol treatment or similar?

 

I am going to completely zero everything tomorrow and using he Des Hammill book set them up as per his guide.

I know this may be a stupid question but are the idle screws the only screws on the carbs to actually make adjustments (other than the synchro screw on the linkage), I thought the book made reference to something like air bleed screws?

 

For info the carbs were stripped and rebuilt last summer and the car has not done much running in that time, which I know is part of the problem.  I really want to sort this myself but am running out of ideas!

sorry I can't help .But good luck getting it sorted..Mike

I am reviving this thread as I am still struggling, and the car failed its MOT again on emissions.

 

 I really want to sort this myself but am running out of ideas!

 

If you were to tell us where you're located perhaps there's a local forum member who'd be prepared to pop round & have a look with you. 

With those readings I would be thinking of other things as well as carb balancing. For instance what is the oil like and the induction system from air filter onwards. Also plug condition and vacuum lines plus timing. All can contribute to high emission readings as can a knackered engine. However if it passed the MOT last year you need to think back on what has been done to the engine that could have affected the readings .

Yes you are right there are air bleed screws to balance the airflow to ensure both chokes of each carb flow the same amount of air at idle (not sure how you can have balanced the carbs without including this parameter!).    In addition to idle mixture screws, other factors are fuel pressure, float height and jet size.  

Edited October 2, 201410 yr by 910Esprit

Thanks for the replies, here are some answers...

 

1) I am in Eastleigh, just outside Southampton.

2) Oil was changed in April when serviced, plugs were deemed OK at that time so not changed.

 

The carbs were set up last summer, annoyingly when a friend helped solve a bad earth he played with them.  The only other parameter was build up in the engine I think through the lack of use and rich running.

 

Going to have a play tomorrow and see what happens.

Sadly Eastleigh is a little too far for me to pop round

Usually when the co goes up, the hc goes down and vice versa. I would be checking all vacume pipes first, clean the air filter and recheck the timing, if the co is high, the mixture screws are too far out I think?

Thats okay Dave, I wasn't after anyone doing the job for me (although it would be nice to be taught by someone who knows wgat they are doing).

 

I am going to go right back to basics and start from scratch.  The mixture screws were certainly leaned down in between the two MOT;s, I was surprised the difference wasn't more. 

Try this link......

I have been attempting to tune my carbs this week with a carbtune and this website tells you what to tweak and when.

Mine is definitely running better now but not at MOT stage yet 

Good luck

Phil

 

http://www.mlmparts.com/media/pdf/carbtune/using-carbtune-ii.pdf

Thanks for the link Phil, I will have a good read tomorrow.

 

I ended up buying a STE synchoniser (the pod like balancer) - this was used on wheeler dealers when they tuned up the Lambo Urracco).

 

I must admit I have not touched the vacuum taps, that I think that is the part I have not got my head around yet.