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Popping and backfires

Discussion in 'Bay Tech Clinic' started by Ian and Shelley, Apr 7, 2019.

  1. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    172
    Location:
    Umina Beach
    Hi all...

    Just bought myself an auto meter to check a few timing bits and pieces...as I have a popping \exhaust backfire when "rolling" down hill...we live on the top of hill, everytime we head out we have a short 2 min drive then a long downhill coast, which is when the popping begins...popping not been noticed when engine running or when lifting off gas in traffic..

    Kombi is running well, its starts and idles good, acceleration is better than I expected, (compared to an old series 3 land rover)...
    I have new distributor points plugs leads etc etc...all valves adjusted to correct settings and general engine running is good...
    Timing correctly set etc...

    But the new dwell meter is giving me a dwell angle reading of 82° .Which can't be correct can it?

    Would the engine run at 82 dwell it wouldn't run would it???
    Could this be cause of popping?

    Maybe i bought a dodgy meter thingy ?

    Any other reasons for popping and backfiring?
     
  2. David H

    David H Well-Known Member

    Messages:
    4,673
    Location:
    newcastle
    Sucking air from an elbow to carbs. Split joins up with a bit of heat. Look closely;).
    Cheers
     
  3. splitbus

    splitbus Well-Known Member

    Messages:
    3,311
    Location:
    Brisbane
    Exhaust manifold gaskets need replacing, (copper rings) or maybe a pulled exhaust stud, try tightening the nuts on exhaust manifold first
     
    David H likes this.
  4. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    172
    Location:
    Umina Beach
    Thanks..

    I have replaced with new all carby elbows and connections, but will recheck and observe ..

    Exhaust has new copper rings, I will retorque all exhaust nuts and recheck..
     
  5. tintop

    tintop Well-Known Member

    Messages:
    470
    Location:
    Canberra
    running lean on one (or both) of the idling circuits will do it too...
    when the engine is at operating temperature pull a wire off one cut off jet and note the reduction in revs then put the wire back on.
    then pull the wire off the other one and it should reduce the same amount.
    if pulling one of the wires kills the engine then the other carby has the problem - blow through the idling circuit
     
  6. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    172
    Location:
    Umina Beach
    Thanks


    Is that the wire for the initial mixture cut off solenoid?

    I also have wire going to the idle mixture enrichment and the central idling system

    [​IMG]
     
  7. cbus

    cbus Well-Known Member

    Messages:
    11,701
    Location:
    sunshine coast
    Popping under conditions described is air leak on exhaust side, lack of back pressure or lean on idle circuit.

    Dwell should be 50 +_ 1 deg for new points and between 42-58 for old points.
    Points are crap now and the wear blocks wear fast so check timing/ dwell every 2k km as they regularly go significantly out of tune before next service period.
    Typically the rubbing block wears in first few days enough to alter timing to make for a stumble at low revs.
    If this , or loss of idle, occurs check dwell before adjusting timing or idle.
    I tend to set new points slightly wide to allow for this.

    Can't say re 82 degree without trying it.
    Prob would run if timing adjusted accordingly.

    With no contact the dwell Meter will show 90 deg.
    Check you have clean contact and the reading is steady.
     
    Last edited: Apr 8, 2019
    Mordred likes this.
  8. Mr Beckstar

    Mr Beckstar Well-Known Member

    Messages:
    985
    Location:
    Bateau Bay, NSW
    Check that your dwell meter is set to 4 cylinders too.
     
    oldman and cbus like this.
  9. cbus

    cbus Well-Known Member

    Messages:
    11,701
    Location:
    sunshine coast
    Yeah.
    I take back much likelyhood of running at 82 deg.
    It would be a dog if it worked at all. ;)
     
  10. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    172
    Location:
    Umina Beach
    Thanks.
    New dwell meter arrived today, dwell set at 45° so old meter was highly inaccurate...

    Corrected timing etc but still plenty of backfiring and popping..

    Will take a closer look at exhaust connections and increase mixture to see what differences it makes..

    Thanks
     
  11. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    172
    Location:
    Umina Beach

    OK....when pulling left wire (from rear) drop of 150rpm...pull right wire off and engine stalls, will not run...

    So i need to adjust the left carby..???
     
  12. Barry

    Barry Well-Known Member

    Messages:
    3,588
    Location:
    Abbotsford NSW
    Holding a tennis ball or something similar to the end exhaust pipe should result in the engine dying.
    It it just keeps running then you have a leak that will result in the popping you have
     
  13. tintop

    tintop Well-Known Member

    Messages:
    470
    Location:
    Canberra
    yep because it isn't running properly on that side (which it has to do when you disconnect the right side)...if it was running properly before it's more likely that you have dirt in the idling circuit than it has gone out of adjustment.

    firstly make sure that the solenoid on the left side clicks with the ignition on (not running) when you pull the wire off and put it back on

    you could try unscrewing the cut off solenoid and blowing through there...if no luck you can unscrew the idling mixture screw on that side (and blow through from the top again)...make sure the o-ring on the idling mixture screw is still good while you are at it
     
  14. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    172
    Location:
    Umina Beach

    Would this be the likely cause of the backfiring of have a discovered an NEW problem?
     
  15. tintop

    tintop Well-Known Member

    Messages:
    470
    Location:
    Canberra
    yes lean mixture will give you backfiring
     
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  16. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    172
    Location:
    Umina Beach

    If I increase fuel mixture on the LEFT side should that fix the problem, or could increasing fuel mix hide a blockage?
     
  17. tintop

    tintop Well-Known Member

    Messages:
    470
    Location:
    Canberra
    yeah, normally that's what you would do when you are setting them up ... but if it used to run properly it's most likely got some dirt in it now
     
    David H likes this.
  18. Barry

    Barry Well-Known Member

    Messages:
    3,588
    Location:
    Abbotsford NSW
    I am more familiar with Weber and Delorto's but if you have a blocked idle jet, increasing the mixture screw shouldnt change things
    That is because the idle circuit is not working at all.

    If you adjust the idle screw you will artificially bring on the main circuit and it will really be out of tune.

    Dirt in the fuel will block the idle jet or water that has entered through the air inlet for the idle circuit forms "jelly blubbers" with fuel
     
  19. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    172
    Location:
    Umina Beach
    Thanks


    Looks like I may have to remove the carby and give it a good clean.....or can I just remove the jet ?
     
  20. tintop

    tintop Well-Known Member

    Messages:
    470
    Location:
    Canberra
    as per post #13
     

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