WWS is finally built, but pulls to the right

[ELF]

Alright! The kit is done despite the german instructions. The tricky parts were the steering linkage and the rear diff, everything else was reasonably easy.

Steering linkage: The wire used was fractured so I had to make my own. I also had to find an appropriately small servo arm. Nicely enough, the servo doesn't need to move very much to have the steering go lock-to-lock. Using an HS81-MG.

Servo saver: Doesn't appear to be enough room for one, and the HPI version is a bit small for my needs. Suggestions?

Rear diff: Tricky to get really smooth, but I've gotten it.

ONLY ONE PROBLEM:
I'm pulling to the right on heavy accel. This is something I didn't expect to see on a 2WD car that was designed only as a 2WD car. If I accelerate more gradually, it doesn't pull. Sounds to me as if the torque is not being transferred equally. Suggestions?