this is my thoughts on high speed taxi, don't do it. I believe aopa or eaa came out with an article discouraging people from doing a high speed taxi. when I finished my rv7 I went and got some fuel, taxied to the runway, got on the runway, put full throttle and lifted off the runway when it was ready to fly. that was my high speed taxi . the 4 can give you a little bit of yahooooo, if taxi is fast. best to land slow and just have fun. one more thought, check your tailwheel, if it unlocks easy it may be your problem. my old tailwheel if it got crud in it, it would not lock and it was a handful when it did it. could be your problem. raise the tail and support it on blocks or something, than go in and put full rudder each way and check each time the tail wheel to see if it unlocked on you, if so that's your problem, fix it.