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Superlight Fuel Drip

Discussion in 'Supersport (1974-2007)' started by Fraser, Jan 9, 2021.

  1. thought there was bit of a petrol smell in the garage and then after warming the superlight up for 10 mins saw a fairly steady drip from breather pipe under the bike. Being a mechanical ignoramus, was after some advice. carb problems? now added fuel stabiliser to see if that helps. any suggestions? cheers
     
  2. Tank nearly full and up on a rear paddock stand?

    That can cause any temperature rise to slightly pressurise the tank and instead of releasing the fumes through the breather, as the tank is tipped slightly forwards by being on the stand the fuel gets into the breather outlet for longer than usual and it can get past the breather valve internal seal.
     
  3. hmm not sure. did open the filler cap to release pressure and, of course, add the stabiliser and seems to be continuing to drip. on a abba stand which would appear to keep it pretty level but you are probably right and tipped forward a touch. will see if it continues. cheers mate
     
  4. First of all, follow breather pipe back to see where it's connected. If it goes to a carb bowl, and there are two tubes per bowl, then come back on here and tell us (or swot up) as it could be overflow/needle valve related (most likely, and usually quite simple to cure) or bowl drain which is often more serious*. If the carb bowls have a single tube each (so two carb drains per bike) then the problem could be either of the two mentioned.


    * the bowl drain has a tapered screw fitted which is used to open and then seal the drain tube but the taper is slender and can lead to overtightening (as hard to judge when tight) which can crack the corresponding taper seat in carb bowl body resulting in a leak.
     
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  5. Chris is correct and details another thing that can cause the drip; however, I have also found that if the breather valve cannot easily let pressure out of the tank, then again with a slight temperature rise the tank can become pressurised which in turn pressurises the fuel lines and if the float valve needles are getting on a bit, they can be forced open enough to let fuel by and overflow the float bowls......unfortunately that can lead to siphonic action and the tank can be emptied via the float bowl overflows.

    Possibly the easiset way to see which case you have, is to turn the petcock off.

    Once that is done and the fuel drip doesn't stop, then my initial idea is probably correct.

    If it doesn stop, then Chris' thoughts would be the most likely.
     
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  6. As said, I've had this. Pressure build up with temp changes, tank full, pushes fuel out of breather.
     
  7. Maybe a wee split in the drain tube running through the tank.
     
  8. Depends where the drip is from.....there are four hoses that it could be from.
     
  9. drip got steadily worse so going into my local tech soon. its only done 20 miles since it came back from them couple months back for fuelling issues. over phone he reckons needles as mentioned above :upyeah: will feed back cheers guys
     
  10. If the drip is not from either of the two smaller hoses that hang down and clipped on the left side of the engine just below the front sprocket cover / near the side stand, then it won't be the carb float needles.

    If it is from the larger hose that hangs down and clipped coming from the front on the right side engine, then that is the tank breather hose.

    If it is from the larger hose that hangs down and in the same clip as above, but coming from the back, that is the tank filler drain hose.
     
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