to shim the needles in the carbs, i have read that i need a M3 washer or #4 stainless steel washer. what's the difference? what are the exact dimensions of the washers that i need?

M3 is obviously metric and that is the inner diameter of the washer.

#4 is an SAE measurement which identifies the washer and not the inner diameter (I think).

This might not help, but I found it:
http://www.engineering.com/Library/ArticlesPage/tabid/85/articleType/ArticleView/articleId/118/Washer-Size-Chart.aspx

In that small of a diameter it will not matter enough wether it is metric or SAE.  M3's are easy to get almost anywhere.  I have about 2000 of them in my hobby room, lol.

make sure they are stainless or brass, so they wont rust in your carbs and feed debris into critical passages.

thanks for the help! i got stainless M3 washers and brass #4. now to decide which to use..