Just got back into emulation and starting reliving some of my childhood again - what a blast!

I'm running the emulator called "Model-B" and I'm "fixing" some of the games I've downloaded that don't boot...

*BUILD !BOOT
001 CH."<enter filename here"
<ESC>
*ACC.!BOOT L
<save IMG file back to hard drive>

Problem is, it's saving them out as 200KB files where the original files were often under 50KB sometimes as low as 20KB.

Is there a utility to allow me to crunch them?