Got the valves adjusted and everything put back together on my Kodiak 400. Took it up the road to test it out and made it about 1/4 mile under 80-100% throttle then it starts surging a little and backfiring and trying to die. Kept it about 25% throttle and as long as I’m on flat road it runs fine. I pull back into my driveway put it in park and it idles and revs without hesitation. Make a hard lap around the yard and no problem. Head back up the road and same thing, about 1/4 mile starts sputtering. Any ideas? If the carb was gooped up wouldn’t I see sputtering instantly under hard acceleration?