What is this and would it cause....

[awayatc]

Hi, hope you got bike sorted out by now, but just in case...had similar issues with similar bike once (DR 250) turned out it was the inlet manifold.The rubber bit which is "glued' on to a steel plate (like an engine mount) was not 100 % sealing anymore....hard to see untill you aplly sideway force with manifold removed...
The way you describe what happened to your bike is exactly the same as what was wrong with mine...
Good luck

[awayatc]

Im going with it probably being this, as when i swapped the diaphragm, needles etc off a carb that had been running fine the problem still occured

have ordered parts

-Squiggles (on his mrs' account)

Hi, hope you got bike sorted out by now, but just in case...had similar issues with similar bike once (DR 250) turned out it was the inlet manifold.The rubber bit which is "glued' on to a steel plate (like an engine mount) was not 100 % sealing anymore....hard to see untill you aplly sideway force with manifold removed...
The way you describe what happened to your bike is exactly the same as what was wrong with mine...
Good luck

[Katman]

As has already been said, the o ring around the needle valve seat can definately cause a problem. If the bike has been sitting unused for a long time the o ring can go hard and then (as awful truth has mentioned) will allowed fuel to seep past and will overflow the fuel bowl.