just failed mot on emissions! how do i get them lower?

Hi,

Just failed the mot on emissions on my 3.5 v8 carb defender.

Was somthing like 3.9% co when it has to be 3.5%.

Any quick fixes to be assured it will go through when I take it back.

A clean air filter and some adjustment to the mixture should help.
I run a car with a webber so just a tweek with the mixture screw brings down the levels if ever they are over, they let me do it while it's still connected to the analyser don't think the know about carbs.

fendy said:

Hi,

Just failed the mot on emissions on my 3.5 v8 carb defender.

Was somthing like 3.9% co when it has to be 3.5%.

Any quick fixes to be assured it will go through when I take it back.

Click to expand...

Like Discool said, clean air filter, also clean flame trap and breather, check/set ignition timing and back off mixture, check carbs are balanced (if applicable). Remove and check condition of spark plugs - should tell you if it is running rich. Best way to get it all set is to use gas analyser (again like Discool said).

Hi,

thanks for the help.

Not a mechanic so dont know how to set offset the ignition timing, how do I adjust the mixture going into the carb and is this easily set up again.

thanks

Hi,

I have looked at the filters and oil and it was all recently done. I have looked at the carbs and can only find one screw on the back of one? Is this the one to adjust the mixture?

thanks

fendy said:

Hi,

I have looked at the filters and oil and it was all recently done. I have looked at the carbs and can only find one screw on the back of one? Is this the one to adjust the mixture?

thanks

Click to expand...

You don't say what cab setup u have but normally each carb will have two screws, one on the throttle rod to adjust the idle the other is the mixture which would be screwed into the body/base of the carb.. sorry but my info is just based on my SU and Webber useage.

Not sure what carbs they are, how could I id them?

thanks

seems I have su carbs.

look the same as here

Rover SD1 Forum Snippet # 20 - SU Carburettor Set-up

can you point out where the mixture ajustment is.

also how do I know if its lean enough? will the engine just cut out when its to lean so just make it just enough for it to run?

thanks

A very good link. You need the mixture to be correct the only 'correct' way is with an analyser as u need to pass the MOT.

As for the adjusting screw look at the info in the link.. but I would think it's no2 or similar in the pic but then could be no1 but I doubt it, that look as if it's the idle screw..

Hi,

So I will need todo this at the mot station whilst plugged into the machine? Can I not just turn it one flat before go down thin not make a difference?

thanks for the help.

Yes, and you could... but make a note of the poisition so you can return back to as it is now if you have to and with twin carbs they have to be the same in adjustment otherwise you'll have a lumpy idle. Multible carburettor installations are a bit of a pain to DIY set up sometimes .
Best to get the MOT station to adjust the carbs using their machine it may be just as simple as a single turn of the screw to bring your emissions back into range assuming that the rest of your engine is ok.