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spitting back through carb

Discussion in 'AJS & Matchless' started by mark375850, Jul 6, 2012.

  1. mark375850

    mark375850

    Joined:
    Nov 2, 2011
    my bike is spitting back through carb at low revs to the point it stops,looks to be rich ,I thought spitting back indicated it's lean,I have changed plugs no difference ,could my timing need adjusting? or any other suggestions?? can't find air leak in manifold either,it has a magnetto but has a good spark.
     
  2. batrider

    batrider

    Joined:
    Aug 9, 2008
    What bike? What carb?
     
  3. mark375850

    mark375850

    Joined:
    Nov 2, 2011
    Hi sorry I have been trying to post a few photos but I can't work it out,anyway the bike is a 1929 AJS M8 overhead valve twin port with a carb that looks like a early amal(but no markings)with a remote bowl,body of carb is bronze I think,will try and post photos when I can
     
  4. Triton Thrasher

    Triton Thrasher

    Joined:
    Feb 10, 2009
    Some carbs that old are "two lever."

    Means you have to twiddle the air lever (sort of choke) almost as much as the throttle. You have to enrich the mixture at low revs.

    Yours might not be like this. Who knows?
     
  5. Rohan

    Rohan

    Joined:
    Aug 26, 2010
    A 29 Ajay should also have a lever to adjust the timing - have you tried pulling it on to retard the timing. ?

    P.S. If its correctly set in the timing dept, you should not even be able to start it without retarding the timing....

    PPS A bronze carb with no markings could be jetted for anything !
    We wait the pics with interest....
     
  6. mark375850

    mark375850

    Joined:
    Nov 2, 2011
    starts easily without choke just need to flood carb,have been playing with it all morning put in a smaller main jet and have played with needle height running better but if I retart spark or try to lower idle speed she still spits back and stops,she is running at a fast idle,I guess about 1000 to 1200 revs . Will wait until one of the children arrive home maybe they can post photos for me.The carb is an amal at least thats whats on the remote bowl running a 200 main jet,can't wait to take it down the road she will fly by the feel of it. ps thanks for all advice keep it comming
     
  7. Triton Thrasher

    Triton Thrasher

    Joined:
    Feb 10, 2009
    The spitting back and stopping problem is highly unlikely to be anything to do with the size of the main jet. It is almost always weak mixture or failing magneto.

    Have you sprayed WD40 or similar around the inlet flanges or clips and the top of the inlet valve guide, while the engine is running, to check for air leaks? Air leaks cause fast idle and spitting back.
     
  8. mark375850

    mark375850

    Joined:
    Nov 2, 2011
    Tried wd40 on inlet valve and carb flange ,no difference mag has been recond and has a good spark so should be ok,should I try altering timing? it runs fine 1200 approx revs it just has a problem when trying to idle slower any other ideas ??
    thanks again for everyones imput
     
  9. Rohan

    Rohan

    Joined:
    Aug 26, 2010
    What was the answer to this bike should have ADJUSTABLE TIMING, via the advance-retard lever that alters the timing on the magneto. ?

    These bikes are almost impossible without a functioning advance-retard system. It should be quite difficult to start without retarding the timing, if this is not the case then the timing needs some serious work... hth
     
  10. Triton Thrasher

    Triton Thrasher

    Joined:
    Feb 10, 2009
    Put simply, it won't idle slowly unless you retard the timing with the lever on the handlebar. To do some riding at more than walking speed, you have to advance it.

    (have I got that right Rohan?)
     
  11. mark375850

    mark375850

    Joined:
    Nov 2, 2011
    I must be the luckiest person alive,was resetting timing(it was 10 degress out) and turned her over and there is something adrift in crankcase by the sound of it so will strip her down and post results just imagine the mess ,can't imagine what it is as had her running but I need to have a look
     
  12. Rohan

    Rohan

    Joined:
    Aug 26, 2010
    Good luck with the loose bit in there then - depends on whether its something already broken or just something spare though ?!!

    You should have been able to adjust the timing for 10 degrees with the Advance-Retard lever though ??
     
  13. Triton Thrasher

    Triton Thrasher

    Joined:
    Feb 10, 2009
    Bit of a wild guess, but if it has a spring and cam cush drive on the drive end of the crankshaft, that can give you a deep kind of clonk if the spring is broken or splines worn.
     
  14. mark375850

    mark375850

    Joined:
    Nov 2, 2011
    Thanks again for all your ideas,have stripped engine,problem is the inner cam bush which is a press fit ,it has drifted inwards and is making contact with the end of crankpin,no damage but will have another bush made with a step in it so it can't do this again,very happy with this result could have been lots of other nasties in there,will keep you posted re progress.
     

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