I agree.

and on the old weedeater brand engines with the rear exhaust and intake are more trouble than it's worth, they're mostly 21 or 22cc and are heavy and awkward, but there aren't a whole lot of them around anymore...

I would look for Echo as they are somewhat easy to find but homelite's and ryobi's are a lot easier to find. Before the economy crashed you could find them on craigslist for free all the time but now that everyone's broke they go for like $15 for a non running engine (usually bad fuel lines or a $5 carb rebuild away from running). The old green 4 bolt backplate weedeater featherlite trimmers are easy to convert, get some side cut pliers and go to town on the back plate getting rid of the extra material and get a hack saw and trim up the fan housing, they end up looking like this:


but I agree with av8tor, they are light but the stock port timing is very low, unless you feel up to some experimentation, porting an engine probably isn't the best idea for your first engine... apparently the new $60 2 bolt backplate weedeater brand units from Walmart are a little better than the older ones, but I like the looks of the old ones better... 4 bolt backplates make for easier stud mounts.