I'm having a similar problem. My 88 idles fine (a little high due to a recent carb rebuild that I have not fully tweaked yet), at low speeds it actually runs very good, better than it did before the carb rebuild. Once I start accelerating I get sputtering and backfires. It does not stall just becomes sluggish and I slow down. I used a Shindy rebuild kit - it was like $23 on ebay. It does not come with directions though and I had at least 1 extra thicker oring but honestly, after the first time cleaning a warrior carb (little experience cleaning any carb), it fired right up. There was a decent video on Youtube about cleaning carbs - I searched warrior 350 carb kit.