One of the things that may help you is a little freebie XP Power Tool called "Image Resizer" that you can use once you save the diagram to your hard-drive by clicking on "Picture Tasks" and then "Export Pictures" in Adobe Reader.
You can download the Image Resizer Power Tool for free
here
Once you have it installed, you can get it to work it by right-clicking on any image that you save on your hard drive and click on "Resize Pictures"(duh...lol)... then it opens up the tool that allows you to shrink or enlarge any image and then auto-saves it on your hardrive.
You can use the preset options or click on"Custom" and choose you own size...and it will save the height and width parameters of the image automatically so the image doesn't get distorted and become useless.
That should give you a large enough image to read...and if you use MS Paint to chop it up and save the chunks into printable sized images...you can use a litle scotch tape, a little plastic wrap, and some old-fashioned determination to create a large enough sized re-usable diagram to hang on your garage wall for future reference.
Hope that helps!