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Beta evo tank breather bleeds


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After several micro-wheelies the fuel is spitting out of this small rubber tube (tank breather or vent) and everything around the cap becomes covered by the fuel.

Maybe I have to connect this tube somewhere or fix the valve inside the cap? I hope that trial bike has to withstand much higher wheelies than my 10-cm tries.

The bike is Evo 4T'12.


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The cap contains a one-way valve which should allow air in as the fuel tank empties but prevent fuel from escaping.

I suggest you undo the cap and allow it to breathe for a while to evaporate any fuel trapped inside then blow and suck on the tube to see if it is working properly.


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Putting the tube in the middle of steering head doesn't help since fuel still goes out - you just don't see it.

I have cleaned the cap tube and valve using an air compressor (blew it from both sides) and it helped, fuel stopped bleeding for a while.

But once I stopped the engine and did some hops the fuel started coming out of tube again. Maybe valve works in a different way when the engine is on because of vacuum inside the tank.

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Be careful so there should be free access for air(or fuel) to get in the tank through the breather to let fuel out into carb. If not you it will lead to fuel starvation on higher rpm and lean condition with risk of overheating. 

My bike had recently experienced that issue. Because I had used old piece of tubing for the breather. After some time it got kinked and was blocked. Bike would seem to be running ok and after a while, maybe 30 mins started spitting coolant and cut off. Engine was unusually hot. I could start it but with more throttle it would die or would barely run on low rpm and overheat. Now everything is back to normal :) I need to get that one-way valve though.

Edited by klonheadd
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I know it is not the best solution, but this is all I can have to keep riding until the fuel cap arrives to me from the UK.

Btw tank still has free access to air and throttle cable is not affected by this attachment. I have ordered new cap that comes with the valve inside so I will post an update on this issue right after the test.

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  • 3 weeks later...

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