How many miles are on your belt? It sounds like you belt is burnt and glazed over. Take the belt off and scrub it hard with a wire brush with some soap and water on it. Take some sand paper to the primary and secondary sheaves, like 150 grit and give that a try. It's possible you might need a new belt.
Taking weight out of the primary would only aggravate the situation because you would have to loosen the secondary spring to control the RPM's, which in turn would run the belt looser.
Shim your secondary so that the belt just sticks out of the secondary about 1/8". Shims won't effect anything else on how it runs.
I run the 031 belt, I had some slipping and burning at take-off so I installed an ODS clutch kit and the problem was gone. Still run the 031, it's a good belt.
Also, I didn't explain that when a belt slips, that will cause the belt to be sucked down into the secondary, just like what you have going on. A glazed over belt will cause that.