I also just put on the HP carb... it went crazy, won't idle just almost goes WOT. Did some research and also found where they say these carbs aren't for high altitude because the needle can't be adjusted. I took it apart to see what they meant. While you can rejet it it doesn't have a needle with notches like the NT carb does. So you can't change the needle position. I'm hoping a smaller jet does the trick.