I have 2010 Bayou 250 that came to me with no compression and smoking. Rebuilt top-end to factory specs. Has great compression and isn't smoking, burning oil anymore. Cleaned the carburetor and Rebuilt it because someone had drilled the seat hole bigger. I looked to the carb because after top-end job it cranked right up and idles smooth. It revs great up to a little over half throttle then it starts busting out or loading up is what I call it. Sounds similar to rev limiter but more of a whaaap whaaap sound. Lil puffs of black smoke and it blackened the new plug quickly. The timing is on the marks, I set intake to .006 and exhaust to .008. I replaced intake boot o-rings and checked for leaks. I checked air filter and air box. NOTHING I do seems to make it any better? It's definitely running rich and I have adjusted float several times. The new jets I put in it are by the book of what came in it. I checked muffler and exhaust for build up. If anyone can help me out, I would greatly appreciate it. Thanks.