How to pass a power series to find_root

Okay I think I understand that nfloat() isn't helping but what about how to prevent evaluation of a function passed as a 
parameter to another function.  makelist(f(5.9b-9, e), e, 1, 100) does not take a long time.  In fact it is pretty fast. 
Something is different about makelist().  I think I remember reading that makelist was "designed for functions" in some 
of the documents on the Wiki.

I have a bffind_root() function that I wrote and when I call it it takes so long that I have yet to see it complete. 
bffind_root() is defined in pw.mac.  It is just a simple binary search.  I have tried all kind of quoting of the f() 
like '(f(5.9,e)) but it does not work.  Typing in f(5.9b-9,e) also never completes which makes sense.

I have changed bffind_root() to take the function name as an extra parameter and that works but I would prefer a better 
way.

This is my power series.

f(x,e):=sum(
    block([hbar : bfloat(6.6260693b-34/(2*%pi)), mu : 1b15, m : 9.109389754b-31],
        if  equal(_i ,0) then
        (
            a : 1,
            acc : 1,
            am2 : 0,
            am4 : 0,
            am6 : 0
        )
        elseif mod( _i , 2)=0 then
        (
            a : 2 * m / hbar^2 * (mu * am6 - am2 * e)/(_i * (_i - 1))
        ),
        if mod(_i , 2)=1 then
        (
            _num : 0
        )
        else
        (
            am6 : am4,
            am4 : am2,
            am2 : a,
            tmp : a*acc,
            acc : acc * x^2,
            _num : tmp
        ),
_num
), _i, 0, 300)$

bffind_root('f(5.9b-9, e), f, e, 4.047b-19,4.4947335b-19,30);  this works fine because I modified bffind_root() to pass 
the function name as the second parameter.

bffind_root('f(5.9b-9, e), e, 4.047b-19,4.4947335b-19,30);  this takes forever.

find_root('f(5.9e-9, e), e, 4.047e-19,4.4947335e-19);  this takes forever.

Thanks for advance for any help.

Rich