Something else that is often overlooked is to make sure your main gear wheels are straight. A nose wheel plane will let you get away with a crooked main gear by just fixing it with the nose steering, but tail draggers won't. I use an incidence meter on the wheels to make sure they are toed in the same amount and then I set the tailwheel to track correctly. If your mains are off and you correct it with the tailwheel, you'll notice that the plane pulls when the tail starts to come up even though it's been tracking straight. A properly set up gear will pull a little left right at start up, then go straight with no input from your until the wheels lift (assuming you're flying off a good runway that doesn't induce some yaw itself).