I have no problem with either the triple unit or the double unit. I would guess that Calzephyr's car is not correctly assembled. My double unit did not have all the clips and tabs correctly engauged and I suspect that if I had I ran it the way it was I would have had similar problems, but I noticed this immediately upon removing it from the box and worked with it untill it was all together. I do agree that the cars would probably run better with a little additional weight. These cars are real sobs when installing the lighting kits. I especially had a lot of trouble getting the triple unit back together. Just getting the single unit shells back on is tricky, There are more clips and tabs, which all have to be exactly lined up and connected, than on any of Kato's previous cars. Add the very complicated articulated joint, with just about more parts to hold in exact position at the same time than I have hands, and you have quite a challenge. I had to take the articulated cars apart several times untill I got them back together correctly and they would run properly.