I'm very impressed with the appearance of the L1 and running but it does have the same pony truck arrangement as on the current 8F , Fowler tank and Stanier tank that I have.And the earlier tender drive 8F.
All of these locos as bought derail the pony truck at one location on the layout.
The pony truck takes a 'set' on curves as mentioned above and at the trouble spot is still hard over as the loco straightens out approaching a L/H straight turnout which is easily negotiated if set to diverge left (the same way as the preceding curve) however the loco cannot go straight on without derailment. Adjusting the back to back and the tightness of the screws doesnt help.
I added some fine wire to the other locos to prevent the pony truck running at an angle to the track (it provides side control) and this has cured the previous locos. The L1 will need the same treatment.
I wish they had a better pony truck arrangement as none of Bachmann's locos with a leading truck are affected.
I was going to buy another one but probably wont now I've had a chance to run this one and discover that the truck is the same as the older locos.