Emissions :0(

[Paul Scott]

Popped my B in for an MOT today, although not actually due until next month but I have been advised on emissions check failure.

Although everything else is OK.

Does my 75B still need emission test?

Thanks in advance
Paul

[Peter Cresswell]

Hi Paul,
All things to do with MOT emissions test are from the date of registration. If the car was first registered before 1 August 1975 the test is purely a visual one - i.e is the exhaust very smokey? It should not be tested using the emissions testing kit. For a registration date of 1 August 1975 up to 31 July 1986 the emissions test is measured at idle speed and should not exceed 4.5% vol for CO and 0.12% vol (1200ppm) for Hydrocarbons. There is no requirement for a raised speed test to be done. These two dates will cover all MGBs.

In both cases the cause of your problem is most likely rich running. First, try cleaning out the dashpot chamber and piston with carb or brake cleaner and make sure the piston rises and falls easily and both are the same. Also the needles wear especially the spring loaded ones, so while you have the piston out for cleaning take a look at the needles for any signs of wear. If all this is ok and you have the HS4 carbs try weakening the mixture slightly by turning the nut underneath the carb a couple of flats anticlockwise. This will raise the jet upwards making the mixture weaker throughout the rev range. Do them both the same amount and then adjust the idle speed to 800 rpm. If the needles show signs of wear they may need renewing. Get them from Burlen or any of the main parts suppliers - they are about £13.50 each + p&p.

The HIF4 carbs are different and the adjustment is internal and controlled by a bimetal strip. They can be adjusted but the screw to do this is sealed (to stop you doing it!) which has to be removed. It is better to follow the instructions for the HIF4 carbs given in the workshop manual (Haynes etc.). If you have access to an exhaust gas analyser that will help get the setting right.

In the case of either carb, a CO reading of around 3.5% is about where it should be to give good power and economy. Remember as well that your car becomes MOT exempt fro 20th May!

[Paul Scott]

Thanks for you informative reply Pete :0)
My B is indeed September 75 and needs the emission check. HIF Carbs fitted.
The car uses no oil or water so no smoke, It is also doing around 30mpg ( I take that as a big positive) :0)
They tried it several times with the lowest reading being 4-9 but as it got hotter it got higher up to 6.
I am aware about the MOT, I was looking for a Brake-steering- ect. check. Didn't even think about the emissions.
Popped into the MOT station at 8o'clock to see if they had any space.Told yes we can do it now, picked up the car from it's dry store 500metres away. Left the car with them, it was still just on choke when I dropped it off. But they assured me it was at normal temp.
This keeps my wife happy as she then knows it "should" be safe enough for her to drive.
I will take you advise and check/clean the chambers,pistons and needles.
This is all new to me, but I will learn as I go along the way.

Regards
Paul

[Vic Butler]

Pete, historic vehicles post 1959 are not automatically MOT exempt. A declaration must be made and this can be done only when the vehicle is taxed after 20th May.
. Vic Butler

[Peter Cresswell]

Vic, I understand that! The MOT exemption form V112 at present (and I've checked it this morning) doesn't have a category for post 1960 cars so it can't be done yet. I have queried this with the DVLA - as it is their form not a DVSA form - and they tell me a revised form will be available on-line and in post Offices to meet the 20 May date.
I intend to exempt my B at the end of this month, and there seems to be several myths surrounding this as it is on SORN at the moment, so I let everyone know my experience. I will have to do the first (VED) tax via the Post Office as they seem to be the method of getting the exemption onto the DVLA system and after that it should be possible to do it on line as all it will need is to confirm that the status hasn't changed and it is still not 'substantially modified'.
I might start a new thread under 'General' in the next few days.

[Charles Farran]

Hi Paul,
Just had my 1980 roadster's MOT this am.It passed with the emissions CO reading just under 3 with HI I F carbs. Last autumn I removed & cleaned the carb pistons but left the mixture screws as set from a couple of years ago even though I removed the carbs off the car ( including adjusting one carb float ) altogether this winter when refusing under the bonnet. I always take the car for a good hard run just before the MOT is due.
Cheers, Charles