Yeah, been there, but with a Yamaha IT250. The slide in your carb is not lined up with the pin in the carbs body so when you start it up, it immediately goes full throttle plowing anything in its path over. I take it it's a Bing or Jichov carb being Czech, look down into the bore where the slide goes and you'll see a pin, your slide will have a groove in it. Just line them up and put it together, operate the throttle and look into the intake end of the carb. You should see the slide move up and, most importantly, all the way down.