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Why does my Kombi backfire when I approach a town and let off the gas.

Discussion in 'Kombi Club' started by John Fenn, Mar 7, 2020.

  1. John Fenn

    John Fenn New Member

    Messages:
    10
    Location:
    York WA
    When driving in the country I usually sit on about 90. 80 up hills, 100 down them. When I come to a town I let off the throttle and the car will often back fire once or twice.
    Could this be tight exhaust valves?
    TIA
    2 litre 914 motor with Haltech fuel injection.
     
  2. Barry

    Barry Well-Known Member

    Messages:
    4,654
    Location:
    Abbotsford NSW
    I would be looking at a leaky exhaust first.
    Hold a tennis ball over the exhaust and the motor should stall
    If it still runs then that is your problem.

    if it dies - start with doing the valves
     
  3. Mr Beckstar

    Mr Beckstar Well-Known Member

    Messages:
    1,112
    Location:
    Bateau Bay, NSW
    Also check for air leaks on the inlet manifold and leaks in any of the hoses and vacuum lines attached to the manifold. They can make it run lean and backfire when you back off the throttle with higher engine revs - just like when your on the highway and slow down for a town.
     
    Barry likes this.
  4. Mr Beckstar

    Mr Beckstar Well-Known Member

    Messages:
    1,112
    Location:
    Bateau Bay, NSW
    Also check the vacuum advance on the distributor is working. You should be getting full advance when you back off the throttle at high engine revs and if it’s not advancing fully it could make it backfire.
     
    tintop and Barry like this.
  5. AC-T3

    AC-T3 Well-Known Member

    Messages:
    1,020
    Location:
    Woy Woy
    Note the original post - 2 litre 914 motor with Haltech fuel injection. Means no distributor and only vacuum line is for brake booster. Soooooo, either leaking exhaust gaskets or an ECU/O2 sensor issue or something somewhere.
     
  6. oldman

    oldman Super Moderator Staff Member

    Messages:
    9,323
    Location:
    Avalon Beach NSW
    Check brake booster and line for leaks.....
    Cheers,
    Mark
     
    John Fenn and Barry like this.
  7. KahunaKombi

    KahunaKombi Super Moderator Staff Member

    Messages:
    21,036
    Location:
    Bracken Ridge, Qld
    Hard to pick but a bad fitting exhaust gasket or the headers are not pulled up enough to make a complete seal on the gasket :rolleyes:
     
    John Fenn likes this.
  8. John Fenn

    John Fenn New Member

    Messages:
    10
    Location:
    York WA
    Thanks everybody, I know what to check now. I did put the torque wrench on the manifold notes, but the exhaust muffler has been on and off a few times so I suspect it is the muffler to header gaskets. Cheap fix hopefully.
     
    KahunaKombi likes this.
  9. KahunaKombi

    KahunaKombi Super Moderator Staff Member

    Messages:
    21,036
    Location:
    Bracken Ridge, Qld
    Just have to work out if you need oval copper gaskets - https://www.mickmotors.com.au/product-exhaust-flange-copper-ring-172ltr-73-78-7851.aspx or square ones - https://www.mickmotors.com.au/product-exhaust-flange-gasket-square-port-straight-7852.aspx ...... then straight or offset - https://www.mickmotors.com.au/product-exhaust-flange-gasket-square-port-offset-7853.aspx

    Generally wise to replace the gaskets when exhaust removed even once as there is no guarantee that it'll seat back squarely on the gasket again ;)
     
  10. oldman

    oldman Super Moderator Staff Member

    Messages:
    9,323
    Location:
    Avalon Beach NSW
    Hopefully and easy diagnosis.....
    When working on my son’s ‘71 many years ago, there was an “untraceable” vacuum leak.
    Turned out to be a failed diaphragm within the booster.....
    Cheers,
    Mark
     

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