It's a long story, with a good ending! I have a Makita RBL500 backpack blower--one of my favorite pieces of equip. Early last spring, ran it one day to blow off my own driveway, put it away, next time I pulled it out to use--a week or two--dry summer last summer, wouldn't start. This would usually indicate a fuel problem. Pulled plug, shot in a spray of choke cleaner--still didn't get a hit. This blower probably has fewer than 30 run hours. I'm a crazy man when it comes to fuel, 93 octane (no ethanol), Amsoil at 50:1, fuel stabalizer, never more than a couple months old. I'm not new to 2-stroke repair--maintain equip for 3 full time commercial guys, part time LCO myself. I worked on this several times over the summer--cleaned carb--diaphram and gaskets all in good shape--carb was spotless. Pulled rope about a thousand times (maybe not so many). New sparkplug, another known working plug, changed fuel lines and filter, pulled muffler--exhaust port looked like new engine, spark arrestor screen clean, and muffler looks new. Tested compression with known good tester--120psi at 2nd pull, almost 150 after 4 pulls. Tested spark with an in-line tester--looked great. Pulled flywheel to see if key had sheared--in perfect shape. Against my better judgement, ordered new carb. a few weeks ago--finally could get it to run--but just barely. Getting tired of reading about this yet--I'm about ready to haul to junk, but just couldn't force myselt to do it. Today, I pulled the muffler, reassembled without muffler, pulled rope and it started and ran like crazy--bout scared the cat to death!!! Now I'm excited!! Blew on the muffler with my mouth--couldn't blow thru it--never tried this before so didn't know for sure, blew it out with compressed air, an felt something happen. Tried with mouth again, air moved freely. Reinstalled muffler and it runs great--smoked like an insect fogger for about 15 minutes--probably from all the many times I had tried to start it!!!. What stopped up the muffler--remember this happend while stored in my mower building. Not a dirt-dobber, muffler was spotless as far as I could see! I'm happy it's finally running, but I bet I've worked 40 or more hours on this blower. Glad it was my own, and not somebody's I would be charging for repair.