Too much cross and/or stagger on the front can do that as well.
1 1/2" stagger across the front is pretty normal, very rarely any more than that.
How much craoss are you running? If you're holding the LF up in the air while going down the straights, it will jerk to the left when you let go of the steering wheel.
Going down the straight, if you have stagger on the rear axle, depending on how much, the karts going to pull to the left, no way around it.
To prove I'm right, put two tires on the axle both the same circumference, it's not going to pull to the left anymore. Well, it may pull to the left, but only if something else is wrong. A bad front wheel bearing, poor front end alignment, a frame that is cracked somewhere, maybe other things.