I recently picked up a kx85 big wheel, my first two stroke. Previous owner claimed it had a fresh top end. The clutch was slipping so I replaced the basket. This made the bike pull hard and it was running perfect. I took it riding all day and had ZERO complaints about the power delivery on the bike.
The next day I go to ride it and it has an awful stumble from mid to high end on the throttle. I cleaned the air filter, cleaned the carb, put in fresh fuel, and tried out a couple different spark plugs and this didn't help. The plug seemed oily so I went two steps leaner on the main jet, checked the float level and did a full carb rebuild. The bike still stumbles throughout the entire power band. It starts up first kick and idles fine.
I'm looking for advice on where to go from here. I'm thinking the top end is wearing out, power valve is gummed up or damaged, or it could be something simple I've overlooked. It doesn't seem like a carb problem, because it ran great before it suddenly started doing this. Any help is appreciated.
