honda crv 2.0 flat spot?

my 2005 honda crv 2.0 petrol has a flat spot when i give it some welly ! driving normally and tootling around it drives like a dream , but when i boot it , it has quite a noticeable flat spot going from 1st into second gear(setting off) & 3rd into 4th (overtaking ).It idles lovely and has been serviced recently . any help appreciated . thanks

glynn
June 2013