My petrol Peugot 309 failed MOT on emissions carbon monoxide 10.55%, hydro carbons 810ppm. Changed plugs, oil and oil filter and air filter- retest CO 10.52% and HC 712ppm. Where to now? Improvement very slight, car runs fine but need MOT. This is a carburettor model not injectors.
wow thats high!no mention of missfireing,so I'll assume valve clearances ok,but dont discount at this time a compression test would'nt hurt.I would at this point go for a carb strip down looking for faulty diaphrams or blocked air jets.renew carb to inlet gaskets and reset mixture's and float heights(faulty float also a possible)either way its massivly over fueling.what are you getting 15-20 mpg?also possible leaking vacum hoses/lines that someone has compensated for by altering the mixture.dont forget to check engine breather.a car this age it might be more cost efective to replace carb with a good unit from a breakers.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.