More carb...
I just cannot believe these guys! The carb on that engine is so VERY, VERY simple! There should be absolutely no need to replace it unless you smashed the thing. As has been mentioned, it could be a clogged filter, or simply a clogged jet somewhere in the carb. If you disassemble the carb and study the body carefully, you can trace all of the drillings and ports and jets in there. Blow through each passage with either compressed air, or Gumout spray (watch your eyes!). If you take your time (something most mechanics cannot afford to do), you will find the obstruction. I can't remember for certain if that carb has it, but some of these carbs have a tiny hole drilled in the side of the main jet tube (that's the tube that sticks down into the float chamber with the brass jet screwed up inside it). If that hole is clogged - and it's easy considering how small it is - you'll get the problem you mentioned. Anyway, check it over very carefully. If you see a dark speck on the surface of the tube, it probably is that hole. I cleaned mine out with a piece of wire off a wire brush. Another thing to consider is to make sure the float valve is working and that it is adjusted correctly. If there isn't enough fuel in the bowl, then you'll also have the situation indicated. Just as an anecdote, I had a problem with my Nissan 5HP last spring. 3 people ( BOAT MECHANICS!) pulled the cord until they were spent, and noone could get even a POP out of it! The guys tried 2 spark plugs, pulled the carb apart twice ("THESE ENGINES ARE SUCH GARBAGE!", changed the gas ( "YOUR GAS IS NO GOOD; YOU SHOULDN'T USE THAT JUNK OIL", ETC.), flooded it with starter fluid, disconnected the kill switch (even though it had a spark!). They then suggested I should give up and get a Mercury engine because these damned things were "garbage" (Funny thing: the Mercury 5 IS the Nissan/Tohatsu with different paint!!!!!). Anyway, after everyone was done tearing me and my engine apart, I took it home. Turned out the piston rings were gummed up and the engine didn't have enough compression to fire the fuel! I installed new rings, a couple of gaskets, and it's been running since with the OLD spark plug, my cheap 2-stroke oil from Home Depot, and regular gas. Cost me about 25 bucks!Good luck!Jim Maroldos/v: Lil' Wass Ett