toilet not flusing properly

[cjcb01]

I bought a flap up flush mechanism. However, I believe something has been dropped into the cistern and has ended up in the toilet and is blocking the flush holes. This means that the the flush is weaker than it should be. The toilet and the rest of the bathroom suite are a cream colour so renewing the toilet is not an option without changing the whole suite. The sink is large and cut away into the wall tiles. Just changing the sink would mean retiling the walls. I have taken the toilet off, turned it upside down and everything else I can think of. Help?

[alavapint]

Have you checked that the flap is being lifted as much as possible, when the operating button is pressed..?
Some of them have a chain linking the flap to the button. The chain has to be fairly tight..!

[cjcb01]

It;s definitely not the flushing mechanism, the flap rises properly.
I can only assume there is a foreign body behind where the water is released into bowl; just tried everything to get it out but without success.