I know several people with Ventures, and others with short track Yamaha's. They all had to do the same.
Yamaha has the sleds set up for 1000 pound drivers. There is no weight on the skis, it's all on the front of the track. Every time you attempt to make a turn, at any speed, the sled wants to fall over.
The front shock in the rear suspension needs to be backed off, loosened, lengthened, or however you want to put it.
Get the sled up on a lift, if you have one, so there is no weight on the rear suspension. Loosen the double nuts at the bottom of the front shock in the rear suspension. I just used a hammer and screwdriver to loosen the bottom nut. You'll be able to back the lower nut off about as far as you can. by hand. Now grab the spring around this shock, with your hands, and turn it until the two nuts meet. Tighten the nuts with the hammer and screwdriver.
You will now be able to drive the sled. It will have weight on the skis and it won't pivot on the front of the track.
Replace your runners right away. Save them for when you sell the sled. I run "Deuce" carbides. They seem to last longer than "Dooleys", and stones don't seem to get caught in the runners.
Enjoy