85 atc 110 carb help!

[hogmuffin]

I'm fixing up a friends 110, and it starts and idles great. Once you get to half throttle, it falls on its face and will die if you don't back off the throttle. Took the carb apart and completely cleaned it. Checked for intake leaks, adjusted the valves, all good. It still did the a same thing. Ordered a new carb from ebay.....put it on and it still does the same thing. I was searching forums and found one that suggested it could possibly be an issue with the spark arrestor and improper exhaust back pressure. Of course I can't find it now. My exhaust pipe is wide open, if there was a spark arrestor in there it's long gone. Im at a loss at this point. Any thoughts or suggestions would be greatly appreciated.

[hogmuffin]

UPDATE: I think i figured it out. Found another post for this exact problem that mentioned the intake leaks can cause this problem. Checked my air box seals and the air box to carb boot, all looked good. found the intake boot that goes from the air box up into the frame was not connected to the plastic intake tube that goes up through the center of the frame. I was skeptical that this would make a difference, and that thing was a pain in the A** to get reconnected. but i got it, and fired it up, engine runs great now.

[shortline10]

Yes the stock carbs need a lot of intake back pressure to run properly so no leaks all the way to the snorkel