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  1. #1

    Join Date
    Sep 2011
    Location
    Belfast N.Ireland (Home of Titanic)
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    3
    Hi Folks



    Been a member for a while but this is my first posting since buying my bike last October. Over the winter I have overhauled the carbs using Randle's kit,replaced coils,leads, plugs and air intake manifolds. I have replaced the brake master cylinder , brake lines, pistons and pads. I renewed the fork oil seals, twist grips, gear selector lever ,clutch cable and lever.



    However the bike is backfiring/popping on startup at low revs. I have started it only on one cylinder (does not matter which one) and the popping is not there. There does not appear to be any leaks around the exhaust manifolds. Is is idling at around 1000rpm but you get the feeling she could stall.



    The only thing I have not done is to check the timing and adjust the tappets.



    Just need the popping sorted. Any ideas guys?
    Honda CX500 (1980)

  2. #2
    Senior Member bandit's Avatar
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    Aug 2010
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    espania
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    Quote Originally Posted by Curley View Post
    Hi Folks



    Been a member for a while but this is my first posting since buying my bike last October. Over the winter I have overhauled the carbs using Randle's kit,replaced coils,leads, plugs and air intake manifolds. I have replaced the brake master cylinder , brake lines, pistons and pads. I renewed the fork oil seals, twist grips, gear selector lever ,clutch cable and lever.



    However the bike is backfiring/popping on startup at low revs. I have started it only on one cylinder (does not matter which one) and the popping is not there. There does not appear to be any leaks around the exhaust manifolds. Is is idling at around 1000rpm but you get the feeling she could stall.



    The only thing I have not done is to check the timing and adjust the tappets.



    Just need the popping sorted. Any ideas guys?
    a warm welcome from spain.i have to tell ya....the best black stuff iv ever had was in belfast airport.



    2 things spring to mind,your acv,s and/or an exhaust leak,both/either of these will produce a similar popping.





    id forget timing unless you have pulled the engine apart.tappets,yes fine,do them with your camchain adjustment as part of your maintenance.

    1981 GL500 , UK MODEL,needing a bit of tender loving care

    1982 GL500 , UK MODEL,my daily ride.



    Andalucia,in the south of spain

    aka spanish bandit

  3. #3
    Senior Member bandit's Avatar
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    ....oh and 1000rpm is a tad slow,yes she might stall,wind it up a tough to 1100

    hth

    1981 GL500 , UK MODEL,needing a bit of tender loving care

    1982 GL500 , UK MODEL,my daily ride.



    Andalucia,in the south of spain

    aka spanish bandit

  4. #4

    Join Date
    Sep 2011
    Location
    Belfast N.Ireland (Home of Titanic)
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    Quote Originally Posted by bandit View Post
    a warm welcome from spain.i have to tell ya....the best black stuff iv ever had was in belfast airport.



    2 things spring to mind,your acv,s and/or an exhaust leak,both/either of these will produce a similar popping.





    id forget timing unless you have pulled the engine apart.tappets,yes fine,do them with your camchain adjustment as part of your maintenance.



    Hi from Belfast,glad you enjoyed the black stuff. The acv's have been changed.

    Curley
    Honda CX500 (1980)

  5. #5
    Senior Member bandit's Avatar
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    Quote Originally Posted by Curley View Post
    Hi from Belfast,glad you enjoyed the black stuff. The acv's have been changed.

    Curley
    black is nice

    curly,check for airleaks at the [new]boots and the carb to airbox joints......the exhaust is clean,yeas,no leaks
    1981 GL500 , UK MODEL,needing a bit of tender loving care

    1982 GL500 , UK MODEL,my daily ride.



    Andalucia,in the south of spain

    aka spanish bandit

  6. #6
    Senior Member Sam I Am's Avatar
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    Aug 2010
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    Kitchener, Ontario
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    Greetings and a belated welcome too!



    Cam chain tensioning and setting the tappets is important and the valves must be done when motor is stone cold so you might want to get that out of the way just to cut down on variables. These procedures are thoroughly covered elsewhere on this forum.



    Popping and backfiring are both certainly carb related. When you did the carbs how deep did you go? Thorough carb mainenance is covered here too or you could get Larry's book on carbs. It is most awesome and removes a lot of the mystery of the common carb.



    Did you do anything with the air cutoff valves on the side of each carb? IIRC, if the diaphram leaks you get popping on the over-run.



    Also, even small air leaks cause grief with erratic behaviour. The weakest link tends to be the rubber isolator between the carb and the head as they are prone to cracking over time. There's also an o-ring that must be in place and decent condition between the aluminum part of the isolator and the inlet port on the head. And lastly, there's the clamps that hold the isolators to the carbs themselves.



    You sound like you're at the frustrating stage of 'almost but not quite there'. You'll get it, just keep asking questions and providing detailed symptoms.
    'An object at rest cannot be stopped!' - The Evil Midnight Bomber What Bombs At Midnight

    1982 GL500 Silverfish
    1982 GL500 TBA
    1972 Triumph Bonneville
    1971 Triumph Tiger (in a basket)

  7. #7
    Senior Member Sam I Am's Avatar
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    And I'm a slow slow slow and easily distracted typist.

    I didn't have much luck with aftermarket acv's so I ended up blanking them off.



    Sidenote: Many carb cleaners will gladly eat rubber bits for breakfast.
    'An object at rest cannot be stopped!' - The Evil Midnight Bomber What Bombs At Midnight

    1982 GL500 Silverfish
    1982 GL500 TBA
    1972 Triumph Bonneville
    1971 Triumph Tiger (in a basket)

  8. #8

    Join Date
    Sep 2011
    Location
    Belfast N.Ireland (Home of Titanic)
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    Quote Originally Posted by Sam I Am View Post
    Greetings and a belated welcome too!



    Cam chain tensioning and setting the tappets is important and the valves must be done when motor is stone cold so you might want to get that out of the way just to cut down on variables. These procedures are thoroughly covered elsewhere on this forum.



    Popping and backfiring are both certainly carb related. When you did the carbs how deep did you go? Thorough carb mainenance is covered here too or you could get Larry's book on carbs. It is most awesome and removes a lot of the mystery of the common carb.



    Did you do anything with the air cutoff valves on the side of each carb? IIRC, if the diaphram leaks you get popping on the over-run.



    Also, even small air leaks cause grief with erratic behaviour. The weakest link tends to be the rubber isolator between the carb and the head as they are prone to cracking over time. There's also an o-ring that must be in place and decent condition between the aluminum part of the isolator and the inlet port on the head. And lastly, there's the clamps that hold the isolators to the carbs themselves.



    You sound like you're at the frustrating stage of 'almost but not quite there'. You'll get it, just keep asking questions and providing detailed symptoms.


    Hi and thanks for the welcome . The carbs received a complete overhaul with new gaskets and ACVs etc. I have checked for leaks around the inlets manifolds and there does not appear to be any. I fitted new o rings to them. I may renew the clamps just to be sure.
    Honda CX500 (1980)

  9. #9
    Senior Member Shep's Avatar
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    Check for leaks elsewhere in the exhaust system.They can be sneaky.I had one hidden by the rear exhaust mounting bolt slider area.



    HTH
    If you change your carburettors or oil filter housing or make any modification to your Motorcycle without informing your insurancecompany you ain't got jack shit on medical if you have and accident

  10. #10
    Senior Member stern-69's Avatar
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    Not sure if its the cause, but I know mine backfired a bit even after I cleaned the carbs. While I never found the cause, it did go away when I ballanced the carbs. Not sure if it was the cause, but aside from the ilde jumping up 800+ RPM, the backfiring stopped. Surprizing what a little "unballance" can do (they were not off by much, but boy did it make a huge difference in the way it runs)

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