I don't really understand shimming. yamaha's seem to have a problem where their skis sit a little funny or something and shims correct that. I think... Have you tightened your limiter straps at all? This will apply more pressure to the skis. Won't help in drag racing but may help your darting. What size carbides you have on it? I found the stock 4"s are good for driving it across my driveway when rain is impending and thats about it.