In the absence of SYS::WRITE-FLOAT-DECIMAL, floating point numbers are output in radix 2. This function is defined in floatprint.lisp and is not available if you run CLISP without a memory image (which you should never do anyway!)

If *PRINT-READABLY* is true, *READ-DEFAULT-FLOAT-FORMAT* has no influence on the way FLOATs are printed.