I agree with what Train Larry said, but one thing you can do is take a straight piece of track and put it on your work bench. Run your 736 back and forth to see if it runs correctly. Put the same amount of cars behind it. The point to this is to see if your problem is your engine or your track. Problems with engines can a lot of time be solved by taking an exacto knife blade and "VERY CAREFULLY" clean out the garbage in the slots between the 3 sections of your armature facing. Take your brush plate off and clean it good with carborater cleaner, replace the 2 brushes and, lube the armature shaft slightly where it goes through the brush plate and re-assemble. In most cases you will see a big difference in how your engine runs.  Barry