What made you think to do that Baz? So does the shroud reduce the drop in pressure over the needle jet, so by you cutting it, you increased the vacuum (reduced atmosphere pressure) to eliminate a lean stumble?
Close the
higher the shroud the richer the mixture will be ie
increases the pressure drop around the needle. The lower the shroud the less fuel is drawn from the float bowl. 4T engines don't really need the shroud as the engine always has a good strong pressure signal, the shroud helps the weaker signal of a 2T.
You'll try a Dellorto one day and get to use either a 3,4,5,6,7 or 8mm high shroud independent of the jet needle/atomiser
