YarnMaster
SubscriberMy 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?
Wizard
SubscriberA 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.
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?
AT REST
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.
Master
SubscriberDidnt 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.
ChatterBox
I understood the air pump had nothing to do with combustion just pumped air into the exhaust manifold.
Master
SubscriberAgree 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.
Master
SubscriberAh - Found this link Land Rover Workshop Manuals > 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.
YarnMaster
SubscriberWithout the Lambda sensor?
Originally Posted by Phil B
YarnMaster
SubscriberBee 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.
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