The 207 and 607 buses will take you there from the Bush and its well worth the trip. £1 entry for adults, and sadly a knife arch to walk through, but after that there is a wide range of food, arts&crafts and music stalls and stages.
Here are some pics from last year, it lasts till 7pm but I suspect there will be festivities in Acton park late into the evening ... maybe see you there!
1700 UPDATE: This year's Carnival has been excellent but after I left I saw an air ambulance land in that general area followed by lots of Police cars .. never a good sign. Updates as and when I get them, in the meantime feel free to leave comments
0500 Sunday UPDATE: It seems someone was stabbed outside the Gala bingo hall on Uxbridge Road just outside of the Carnival. Police describing the incident as "nasty" but it doesn't at this point seem to be fatal.