A Walbro carb is easy. I picked up a Homelite string trimmer with a 30cc engine out of the garbage a few months ago. I went to the Homelite website and I think they will want to sell you a whole carb - not sure. For example you can't just buy a crankshaft you buy the crankshaft, crankcase and main bearings all in one shot. I am about one mile from a small engine repair shop and they can get me any Homelite parts I need. Check your yellow pages. Your Walbro carb may just need a good cleaning. I use lacquer thinner or you can go to an Auto parts store and purchase carb cleaner but it's about the same stuff. Whatever you do DO NOT GET ANY RUBBER/NEOPRENE PARTS near the lacquer thinner or it will turn the parts to junk. If you have jet orfices to clear I recommend a gas welding "tip cleaner" available at any welding supply for a couple of bucks. You'll get about 25 different size wire cleaners that won't damage the orfices of jets in your carb. I wouldn't just poke at the jets with a piece of wire. After you are comfortable with your cleaning blow out all the passages with compressed air if you can. Your carb may have a rubber diaphram which will probably be ok. Hold it up to a bright light and look for any holes and examine it for any cracks. Repace as needed. A carb rebuild kit is a good and cheap insurance policy.

Good luck,
Bill