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Title: MOT emissions test Post by: RRomanis on 17 May, 2024, 09:26:47 PM Hi all
At a recent MOT my S3 recently struggled on the missions test, specifically the HC (hydrocarbon) levels. It seems there’s a set target level for all petrol vehicles by age category. Has anyone else had a similar problem with their Fulvia and there any easy way to remedy it? Noting that the cars are MOT exempt but I find it a worthwhile exercise to have someone else look the car over once a year. Thanks Title: Re: MOT emissions test Post by: neil-yaj396 on 18 May, 2024, 10:45:32 AM If it fails the HC test doesn't that mean that it's running way too rich? Good tune up of the carbs should sort it unless of course they are really warn; jets spindles etc.
Title: Re: MOT emissions test Post by: Dave Gee on 18 May, 2024, 06:03:18 PM Having just had my 1972 Fulvia MOT'd yesterday, I understand that the MOT is purely a checklist of visual inspections. Mine did not have an emissions test (none of my classic cars do,) as they would not meet the emissions requirements of much more efficient modern engines.
Dave Gee Title: Re: MOT emissions test Post by: dhla40 on 19 May, 2024, 07:49:46 AM The last MOT emission test I had the limits were 4.5% CO and 1200ppm HC, these are related in that as CO goes up HC comes down so if you have CO below 4.5 you might be able to tweak the mixture a bit richer to help bring the HC down.
Sean Title: Re: MOT emissions test Post by: RRomanis on 20 May, 2024, 07:34:56 AM Hi all
Thanks for responses so far. A follow up question, as my interpretation of a couple of the responses seems to contradictory. My understanding was that is the HCs are to high, I’d need to turn down the mixtures. This seems to be implied in 1 of the responses. However, a later response suggests the opposite ie turning UP the mixtures in order to reduce HCs. Can anyone confirm definitively please? Thanks Title: Re: MOT emissions test Post by: dhla40 on 20 May, 2024, 08:49:54 AM You need to find an MOT garage that will let you fiddle with the carbs during the test, most places are only used to modern cars and have no clue. Luckily my local was happy for me to adjust and it may have been a calibration issue with the tester they were using but my CO was 3% with high HC and by tweaking the CO up to 4.5 it brought the HC down.
Sean Title: Re: MOT emissions test Post by: Beckerman67 on 20 May, 2024, 09:44:57 AM Having just had my 1972 Fulvia MOT'd yesterday, I understand that the MOT is purely a checklist of visual inspections. Mine did not have an emissions test (none of my classic cars do,) as they would not meet the emissions requirements of much more efficient modern engines. Dave Gee Just found this on the Government Website if it helps: "Petrol before 1975 tested by sight" Title: Re: MOT emissions test Post by: Jaydub on 20 May, 2024, 10:31:02 AM Hydro carbons are unburnt fuel caused by an out of tune engine, not necessarily a rich mixture. It could be uneven compressions, badly seating valves, tight valve clearances, worn spark plugs, air leaks, incorrect ignition timing etc etc. As has been suggested, it may help to adjust the mixture to get the engine to run more evenly, but everything else needs to be correct first and then balance and tune the carburettors. Also make sure the engine is fully up to temperature before the emissions are checked, and not having sat around waiting for the test to be carried out. Most MOT testers, especially the younger ones, have no knowledge or understanding of carburetted engines.
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