sounds like you are overjetted.... my Newport does the same thing with anything larger than a 60 jet..(with the plug out on the back of the airbox or a Hi Perf a/f) or a 58 jet with the plug in and that's with a Biturbo... the stock jet is a 50 with a Stock pipe and the plug in the airbox..
When I was running a stock pipe.... I had a 60 jet in it and it did the exact same thing you describe... try a 54...52... or a 50 and I bet it will take off just fine when you twist the throttle open!
It also makes a difference what size manifold you are using... I got better low end with a smaller (12/14mm) intake than with a 15mm and the 15mm carb really dumps a lot of gas in the piston... it may run better with a 12 or 14 with the stock pipe!