The ST has had this a while, and after the rebuild it is still there. When I fill up the bike is transformed. As the tank gets lower the lumpiness increases. I have changed the fuel filter and cleaned the inside fuel cause. I checked the vent and cleaned that all out. Any clues?
Do you hear a slight 'hiss' if you open the fuel filler when the level is low? If so then that would point to the breather still being blocked somehow. I appreciate you've already cleaned the vent out but did you blow it through with a high pressure line? I had it where some stubborn dirt has lodged halfway down the vent tube and came out only when the vent was blasted through with a compressed air line. Just a thought as it does sound like gradual fuel starvarion.
I did blow throw with pressure and I can't hear a hiss. Thinking of taking the flange unit out and cleaning checking everything.
Worth a shot mate. Also you could try opening the filler next time it starts to run rough and see if that makes any difference. At least it would rule out a blockage in the vent if the problem persists.
cant remember how the vent works now! is it simply through the cap body or is there a pressure relief valve?
If I recall correctly, it's through the filler neck/recessed seat, where there's a hole towards rear. This connects to a breather tube that exits on the bottom right of the engine.
