URL encode everything in a url but the = signs

I jave one long string with pairs of parameter and values concatenated like so:

<cfset mystring = "variable1=$13&variable2=http://&variable3=z">

I need to url encode the parameter and parameter values... but the = equal sign should not be encoded.

Do I have to split the the string up.

I also can't have the url encoded function encode . periods in a url? I'm not sure why it does it by default