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On no.......Black smoke followed me home today

Discussion in 'Technical and Troubleshooting Torque' started by Curiousity, Jun 8, 2008.

  1. smells like petrol....burning petrol, very strong.

    only when im on the go and when i first start it up

    no change in power (that i noticed) and still sounds the same

    very thick and very black

    pretty sure its coming from my exhaust. But i will have to wait til my brother comes over to double check that (hard to see when im the one riding it)

    cant really say much more at this moment. Thats all i have for now, too dark to see anything outside.

    Full service just three months ago!

  2. Yep black smoke and smelling of petrol is definitely caused by too much
    fuel getting into the engine. As said, make sure your choke is switched
    off, and if your fuel tap has a "PRI" position make sure it is NOT at PRI, but at "ON" or "RES" instead.
    Then take it for a ride and check it.
    If that doesn't help you could try putting a little fuel system cleaner
    (eg Wynns Spitfire, Nulon Carburettor/Fuel injection Cleaner)
    in the fuel tank and riding it for a tankfull, to hopefully clear away any
    gunk inside.

    After that it becomes time for mechanical investigation and pulling stuff apart.
  3. Hotcam may be right - too much fuel in the mix. Check choke first, then air filter, and other things on Hotcam's list.
    But another possibility is air/fuel mixture escaping unburnt from the combustion chamber. This can be caused by valves not closing properly (valve clearances have completely closed up) and mixture being pushed out of the combustion chamber. This can be rectified with a few hours labour. Another (worst case) scenario is broken or seized valve.
  4. It would really really help if you told us a few simple things like what make and model bike you ride.
    Is it a 2 stroke or a 4 stroke motor for starters?
  5. Hey guys,

    Thanks for all your advise so far! My bike is a 1991 GPX 250, 4 stroke.

    I looked under the bike today and there is no leaking and my feul tap is in the "ON" position. When i started it this morning there was a lot of black smoke but stopped shortly after it was running (well not completey but not as thick).

    I will pass the advise onto my brother and get him to check it. I dont know much about the mechanics of a bike. I dont want to book it into a mechanic though!!!!!!!
  6. It's most 99% likely a rich fuel mixture which causes the black smoke you describe.
    May need a few adjustments to get the right fuel mixture.