Pitching on yeast cake

I have pitched onto a primary yeast cake before(with rapid action),but that was after i had transfered the beer to a secondary(brewing bucket with lid and airlock...but it worked ok) after 5 days.
This time i will be pitching onto the cake from a brew that has been sat in the primary for 2 weeks.
Will this cause any off flavours(i have read about leaving beer on the cake for to long)?

Nah...it should be OK. I've pitched onto two week old yeast cakes many times and plan to do so this weekend.

The issues with beer sitting on the yeast take longer to become problems. It wouldn't affect your new beer, anyway...if anything it would affect the old beer. The yeast cake will multiply back to saturation population when you put fresh wort on it, and it'll taste fine.

The only possible issue is if the beer has been sitting a long time and/or is high alcohol, there may not be enough viable yeast. Two weeks is almost never a problem, though.

Cheers

You'll be fine. Two weeks isn't all that long. Unless the brew that's in there now tastes off when you transfer it, you're good to go.