In general when an engine revs up and down and dies, it's asking for more fuel. Find the enrichment adjusting screw and turn it counter-clockwise about 1/16 inch turn. If that helps some, try revving the engine from idle to full throttle and see if it picks up and runs ok. If it helps some, but not enough, turn another 1/16 until you get it to where it will run and throttle up ok. Hope this helps. Wouldn't hurt to clean the carburetor or at least spray it out with carb cleaner.
