MetaPost stack size exceeded

Hello,

I have a problem with metapost in tetex (2.0.2). When i run mpost on a function
which has more than 18 recursions, i get the following error message:

    ! MetaPost capacity exceeded, sorry [parameter stack size=150].
    
I didn't find any parameter in the texmf file which had as a value 150. I
changed some other parameters (stack_size, param_size, stack_size.mpost, 
param_size.mpost, ...) to bigger values, but without any luck: i keep on
getting the exact same error message. 
Does anyone know how to solve this problem ?

thanks in advance,
Remko