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As can you see my new air filter(that was original yellow color)is turned to black after only 2000 km due to a leakage in the exhaust manifold,which caused the burned gases(probably unburnt gases from rich air/fuel mixture)to be sucked through the air filter.The filter don't have any debris or dust besides the black soot.Can this soot clog the filter/reduce its effectiveness?Should i replace the air filter though it is new?(less than 2000km).The car is with carburetor. Thanks.

  • While you should probably replace the air filter, you really need to figure out why it's doing it in the first place. If you don't, you're going to be replacing the filter every 2kkm instead of the 45kkm (guestament) it should be changed at. Since this is carbureted, you should consider doing a tune up and adjusting it. I don't think the exhaust should be recirculating back into the carb, should it? I don't remember carbs having an EGR function to introduce exhaust back into the intake. Commented Mar 2, 2023 at 15:14
  • Is this fumes from the crankcase ventilation system?
    – HandyHowie
    Commented Mar 2, 2023 at 15:32
  • @HandyHowie,the black color is dry and the fumes from the crankcase ventilation are bypassing the air filter and not going through it.So i guess that it is related to the leaked manifold,i can't find something else.
    – xchcui
    Commented Mar 4, 2023 at 10:38
  • @Paulster2,I didn't mean that it recirculating as it doesn't have EGR function,indeed.While i revv the engine to high rpm under the hood,a cloud of smoke was leaked from the exhaust manifold(also the smell get inside the car),so i meant that this smoke might sucked through the filter with the air and clogs it.And yes i have a rich mixture.
    – xchcui
    Commented Mar 4, 2023 at 10:38
  • You need it find the cause. What is the the year make and model ?
    – Darhus
    Commented Mar 5, 2023 at 17:21

2 Answers 2


Yes, you should replace it. The black color shows that the filter has trapped the particulates that tried to enter the engine. At this point the filter is effectively clogged.

  • Thanks.So,do you mean that the unburnt gasses(rich mixture)alone,which leaked from the exhaust manifold can clog so fast the air filter even that the car made less than 2000km and in no dust condition?is it actually a carbon particles(soot)at the photo?
    – xchcui
    Commented Mar 2, 2023 at 14:24
  • 1
    Whatever is coloring the filter black, and it's likely "soot" (i.e. unburned hydrocarbons), is clogging it.
    – jwh20
    Commented Mar 2, 2023 at 14:33

Hope this helps. On older carburetor unit the air cleaner used one of two sources for air intake. On the snorkel part of the air cleaner was a vacuum motor ( thermac valve ) that switched the intake air from a shield around the exhaust manifold via a hose to air intake that was not from around the exhaust manifold . I would check the valve in the snorkel part of the air cleaner to make sure it's not stuck to the exhaust mode . I also suspect an exhaust leak under that exhaust shield

  • Yes the carburetor has 2 sources for air intake(cold and hot)and they work as you mentioned,by vacuum that open/close a valve.This part is not working properly indeed,but even if it was completely stuck to the exhaust mode,i don't think that it was causing the air filter to be black unless there is a leakage in the exhaust manifold and as you mentioned,apparently the leak is under that exhaust shield.Thanks it helps.
    – xchcui
    Commented Mar 8, 2023 at 17:39

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