110 V8 failing the emission test

[lebanon]

My 110 with a 4.2 L engine fitted with SU carbs fails the MOT on yearly basis due to the excessive CO emission.

This problem is recurrent for all cars still running on carbs, to solve this problem the carbs are set very lean to a point that the car is barely drivable.
I had another approach for this issue; I have a set of SU carbs tuned to pass the emission controls of the MOT. The swapping between carb sets is not difficult but time consuming.

I am thinking of installing a 3 way limiting valve that will be used to divert most of the fuel feed to the fuel return line that will be equipped with a non-return valve to the carbs side.

What do you think of this solution? Will it make the carbs run lean and avoid me the hassle of swapping the carbs for the yearly MOT check-up?

https://www.aulro.com/afvb/images/imported/2014/10/945.jpg

[Phil B]

A catalytic converter on the exhaust will help (thanks Wheeler Dealers)
also try a carb rebuild kit and go leaner on all the jetting. Jet kits are available in the States and UK.
Only way you can really tell if it is working is with an exhaust gas analyser at your local mechanic.
Phil.

[n plus one]

Wouldn't have thought reducing fuel line feed would lean out your jetting? Would just expect it to create fuel starvation/stuttering at high throttle settings?

[bee utey]

My suggested fix would be to fit an electric solenoid valve to meter a small amount of fresh air into the inlet manifold from the air cleaner at idle. Switch on = low emissions, switch off = driveable.

[BilboBoggles]

Didnt some versions of the v8 reduce co by pumping air into the exhaust ports. Usually the whole system is clogged up or removed by now, but perhaps with a suitable air pump that would help ensurw full combustion.

[djam1]

I understood the air pump had nothing to do with combustion just pumped air into the exhaust manifold.

[BilboBoggles]

Agree and the purpose of that is to ensure that any uncombusted fuel - including CO is fully oxidised - for example to CO2. The later non air pump version only really operated during sudden throttle closures where the mixtures are typically very rich for a short period, there was a butterfly (Gulp) valve that only admitted air during those periods to ensure the fuel burnt right at the exhaust port. But the early versions I seem to recall had a vane operated pump. Almost always those ports or the one way valve failed, usually the pump was worn out after a few years and then most people just disconnected the pipework and plugged the ports with brass plugs.

It's the same principal that those triple burn wood stoves use, they pass oxygen into the hot exhaust to ensure that any incompletly oxidised fuel or combustion gases are fully oxidised.

It would be interesting to see what happens if you connect an electric air pump, a set of one way valves and associated pipework to the air ports - if it has them - and then switch the pump on and off.

[BilboBoggles]

Ah - Found this link Land Rover Workshop Manuals > Discovery II > EMISSION CONTROL - V8 > DESCRIPTION AND OPERATION > Secondary Air Injection System (http://workshop-manuals.com/landrover/discovery-ii/emission_control_v8/description_and_operation/secondary_air_injection_system/)

such a system would ensure you keep the right tune on those carbs and should solve the emission issues.

[lebanon]

Without the Lambda sensor?



A catalytic converter on the exhaust will help (thanks Wheeler Dealers)
also try a carb rebuild kit and go leaner on all the jetting. Jet kits are available in the States and UK.
Only way you can really tell if it is working is with an exhaust gas analyser at your local mechanic.
Phil.

[lebanon]

Bee Utey, this is the most interesting and easy to fit option.

correct me if I am wrong but electric solenoid valves operates either on or off. For such an application I need to be able to stage regulate the quantity of air in the inlet manifold to reach an acceptable mixture that keeps the car idling with and give the low CO reading.



My suggested fix would be to fit an electric solenoid valve to meter a small amount of fresh air into the inlet manifold from the air cleaner at idle. Switch on = low emissions, switch off = driveable.

[lebanon]

Absolutely correct, I have closed the fuel needles in order to have an acceptable reading of the CO but as you said fuel starvation occurred to the extent that it was not possible to accelerate properly .

The system I am thinking about will be used just for passing the MOT emission test.


Wouldn't have thought reducing fuel line feed would lean out your jetting? Would just expect it to create fuel starvation/stuttering at high throttle settings?

[Lotz-A-Landies]

What would happen if you shut off fuel to one carb for the MoT?

Would run very lean.

[lebanon]

Lota-A-Landy, the engine will be running on 4 pistons in a shaky manner that will intrigue the MOT personnel.

[bee utey]

Bee Utey, this is the most interesting and easy to fit option.

correct me if I am wrong but electric solenoid valves operates either on or off. For such an application I need to be able to stage regulate the quantity of air in the inlet manifold to reach an acceptable mixture that keeps the car idling with and give the low CO reading.

Yes a solenoid is either on or off but you can add a small needle valve inline as well for the fine adjustment, even a fish tank bubbles adjuster valve might do. Suitable vacuum solenoids are used on older emissions control systems so shouldn't be hard to salvage off something. Some early EFI RRCs used them to speed up the idle with the a/c clutch. Getting the air evenly to both carburettors may involve drilling a small fitting into each carby spacer and using a tee piece between them. If you got creative you could get a 40 - 50C thermostatic switch to operate the solenoid so that the vehicle was legal whenever it was warm.

Random pics of parts off google:

https://www.aulro.com/afvb/images/imported/2014/10/873.jpg
https://www.aulro.com/afvb/

https://www.aulro.com/afvb/images/imported/2014/10/874.jpg

[Lotz-A-Landies]

Lota-A-Landy, the engine will be running on 4 pistons in a shaky manner that will intrigue the MOT personnel.Are you absolutely sure that the air chambers to each bank within the manifold are not connected?

[lebanon]

a 100% sure, I learned it the hard way with a leaking chock system seal that fouled 2 spark plugs on each bank.

one carb feeds piston 1,4,6 and 7 and the second carb the remaining.


Are you absolutely sure that the air chambers to each bank within the manifold are not connected?

[AndyG]

Water/metho injection will lower emissions if you can get it right

[1950landy]

You could put lean needles in the SU's when going for the test or adjust the needles lower into the jets. Also retarding the ignition will help. The air pump system was a cheap Solution back in Leyland's day & pumped fresh air onto the back of the exhaust valve & burnt the unburnt fuel in the exhaust system. A lot of the Jap manufactures used this system. I remember on the Mini's people would take the belt off to discount it but the exhaust gases would get into the pump & seize it & when they wanted to sell the vehicle they would have to get a new air pump & other parts.

[lebanon]

I found this valve at the A/C hardware supplier.

https://www.aulro.com/afvb/images/imported/2014/10/872.jpg

The technician assured me that it will answer my need for regulating an airflow.

The next step is t fabricate thick carb spacer from teflon polytetrafluoroethylene (PTFE) resin. to be able to install small fittings as you suggested, those will be blanked and the valve taken out once the MOT is passed.


Yes a solenoid is either on or off but you can add a small needle valve inline as well for the fine adjustment, even a fish tank bubbles adjuster valve might do. Suitable vacuum solenoids are used on older emissions control systems so shouldn't be hard to salvage off something. Some early EFI RRCs used them to speed up the idle with the a/c clutch. Getting the air evenly to both carburettors may involve drilling a small fitting into each carby spacer and using a tee piece between them. If you got creative you could get a 40 - 50C thermostatic switch to operate the solenoid so that the vehicle was legal whenever it was warm.

Random pics of parts off google:

https://www.aulro.com/afvb/images/imported/2014/10/873.jpg
http://www.sdindustries.org/images/needle%20valve4.jpg

https://www.aulro.com/afvb/images/imported/2014/10/874.jpg