How do you detect air leaks?

Discussion in 'Motorized Bicycle General Discussion' started by Cr9ck, Oct 28, 2008.

  1. Cr9ck

    Cr9ck New Member

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    HI I don't know much at all about engines or anything. My question is how do you detect air leaks? Is it dangerous to have an exhaust air leak? Im using exhaust paper for a few days because my pad fell apart and Im nearly broke.
     
  2. Spunout

    Spunout MB Builder Extraordinaire

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    with a warm, idling engine, flip the choke all the way up to ON. if it doesnt die right away, you probably have one.

    where is it coming from? there's lots of places....carb/intake, intake/jug, head/jug, jug/base.

    set your idle a little faster than normal. spray some brake wash or carb cleaner around those parts. if the idle goes up or down when you hit a certain spot, thats where the leak might be.
     
  3. Cr9ck

    Cr9ck New Member

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    yeah somewhere seems to be leaking as it is running really hot. i wonder if it is just my exhaust? I flipped the choke up and it didn't die so yeah. Is there any way to run the engine without moving the bicycle? I don't have a stand.

    How long does it take to kill it if it has leaks?

    Thanks
     
  4. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

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    If it has an air leak and you run it too much, you will kill it.

    If you mean when spraying, sometimes you'll barely hear it speed up or slow down.

    Just fire it up, have a helper hold the clutch in and spray around the places like the carb to manifold joint, manifold to cylinder gasket. It's easier to just take off the manifold where the two bolts hold it on, smear a thin film of RTV or any other silicone on BOTH sides of the gasket, and re-install.

    You may want to check the top of the carb too. sometimes they are loose and suck air in there too.
     
  5. Cr9ck

    Cr9ck New Member

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    Is the manifold where the carb goes into the engine? How can I fix the top of the carb if is that? Would the exhaust gasket be an issue?
     
  6. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

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    The exhaust gasket isn't a major issue, but should be fixed if it is leaking.
    The manifold is the "neck" between the carb and the cylinder.

    As for the top of the carb, just make sure it is tight.
     
  7. Cr9ck

    Cr9ck New Member

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    How do I start the bike without a stand then? Do I just hold the seat and rotate the pedals?
     
  8. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

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    Get on, pedal, release the clutch, and when it's running, ride back to the workshop and pull in the clutch and lock it, or hold it and have a helper spray the goods.
     
  9. Cr9ck

    Cr9ck New Member

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    Yeah I figured it out. it only runs if i really choke it. I sprayed wd-40 around where the carb connects to the intake manifold and it revved up the first time. I tried it again and this time when I hit it with wd40 it revved down each time I did until it cut out... The intake manifod itself seems fine and the part where the carb connects to it is tight.

    I have also detected that around the primer pin near the screw gas is leaking. Perhaps it is leaking out the side of the carb. I tightened the screw but I think it is still leaking.

    Any help would be greatly appreciated.

    Thanks
     
  10. old motorbike

    old motorbike New Member

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    Loosen the carb retaining bolt and slide off the carb. Clean the manifold neck and inside the carb where it slides on with carb cleaner, brake cleaner, even alcohol. It just needs to be dry and clean. Smear on a coat of RTV silicone to the manifold neck and slide carb back on over it and tighten bolt. Let it cure for a while and see if it still has an air leak.

    The primer will always leak some.
     
  11. deacon

    deacon minor bike philosopher

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    If you haven't sealed your manifold you probably have one. If you haven't sealed it I would it can't hurt and it would probably help.
     
  12. Cr9ck

    Cr9ck New Member

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    I put some on but I didn't clean it. It seems to be working?

    Now my problem is the head gasket I think. Its right below the spark plug and 4 bolts/nuts. Its leaking out gas/oil. Do I just tighten the bolts?
     
  13. Spunout

    Spunout MB Builder Extraordinaire

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    i dont know what the torque specs for that is. perhaps, what i'm going to suggest next will send shivers down the spines of some MB'rs, but when that happens and the nuts/bolts are already tight, i use a flathead screwdriver and stuff JB-Weld in the crack. the JB will NOT be a problem later on, if you have to remove the head. it gets brittle and flakes off without much trouble.

    right, wrong, whatever. it works for me.
     
  14. deacon

    deacon minor bike philosopher

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    Around here somewhere is the specs for that torque but are you sure it isn't coming from around your spark plug. If you have had the plug out several times it might be the compression gasket on the plug gone. If you haven't had it out and it is tight, then it might be the head gasket. More likely the plug I think
     
  15. Cr9ck

    Cr9ck New Member

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    wouldn't you physically see gas around the spark plug? I See it bubbline and air coming out near the head gasket so I am 99% sure it is that. Do I need to get a guage to test my torque on these parts or can I do it till its tight?
     
  16. Smoothe

    Smoothe New Member

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    I thought I had that same problem but it turned out to be the exhaust. I cut a new exhaust gasket and grinded the pipe plate where it bolts on (so it's flat and level) and that seemed to work.
     
  17. Dave31

    Dave31 Moderator
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    One way I like to check for any vacuum leaks is to use propane... If You use a small propane bottle with a hose; Turn the propane on and while motor is running, run the hose along areas that are known for leaks and listen for the RPM to change.

    :ride2:
     
  18. deacon

    deacon minor bike philosopher

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    When I replaced my piston rings I borrowed a torque wrench from the auto parts store.
     
  19. Cr9ck

    Cr9ck New Member

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    Well I hope I didn't overtighten. I don't know if its still leaking from there put its hot as h3LL. How can I check it? I tried spraying the wd 40 into it and It didn't rev up or anything.
     
  20. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

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    Let the engine cool, grab your wrench by the head so the socket is coming out of the middle of your palm more or less and tighten it really well.

    You shouldn't be able to strip anything holding the wrench like that.

    If you have only box or open end type wrenches, hold it very near the working end and tighten the same way.
    Tighten them in a cross, or "X" pattern.
     

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