I found it used to ocur when driving faster, ie dual carriageways n stuff. Mostly when it was damp/foggy, but not when it was really cold.
I put a bit of elephant tubing from the cold air intake to the exhaust manifold, which warmed the cold air up a bit, and helped. Recently my garage told me to mod the airbox a bit, such that the flap is always in the hot position, by using a screw. He told me it pretty much cured carb icing, and that even in idsummer in traffic, it still wont overheat! So, i gave it a go, and it certainly does help! It does take a bit longer to warm up though... but i drove in fog, and it didnt even splutter

this pleased me! it has stalled once or twice, but only when its been cold, and i havent warmed it up fully, as the air intake will obviously still be cold!