I just bought a 1980 suzuki gs450. Once you bring the throttle to 2000 rpm and then let off the rpm's take off to 3000-4000 rpms. Thottle cable is not hanging up.
Everything looks to be in order in the carbs. shutting the bike off and immediately restarting everything returns to normal. until you touch the throttle again. what am I missing?  

So, you're saying that as long as you are very careful to never let the engine get up to 2,000 rpm, you can accelerate up through the gears and no matter how much you twist the throttle, the carbs always returns to idle settings and the engine always ceases to accelerate when you do. In other words, no matter how strongly or gently you accelerate or decelerate, the bike responds perfectly as long as you keep the rpm below 2,000? But even when accelerating very gently, just slowly drifting to faster mph in high gear, when the tach crosses the 2,000 rpm mark, as soon as you back off the throttle, it's like a ghost twisteded the throttle to wide open and you have to hit the engine cutoff switch to slow down?

regards,
Joe  

One of the things that may help the gearheads is throttle position at time of incidence. Take a couple of pieces of blue painters tape, put one on the grip, and one on the frame.
Put a thick line on the one on the frame. Match it on the throttle piece, (with bike turned off) crank the throttle full, make another mark.
Now mark off 1/2 way between them, then mark the 1/4 points.

Now, when the problem occurs, you can say what throttle position you were at. There are about 4 different jet circuits on a carb'd bike. This test will tell you which one of them is involved.
Plan B is to dig out the Cruiser article on carb tuning, and do the a-z. BTW, it also gives the approx cutoffs for each jet circuit.