I had the same problems when I got mine last year...
I bought the Apico steel plates (about 20 quid) and PJ1 Ultra Light 75W, from BVM and it sorted it right out.
...not sure which did the trick though, as I did both at the same time.
Another mod that I'd recommend are the footpegs - I put S3 Hardrock's on mine and they're much better than stock.