I'm just getting started again after many years and got the HO McKinley Explorer for my grandsons.  I set it up and ran it, but I fofund that on a right hand turn, the cars broke away from the engine.  I switched cars to see if there was a problem with the coupler on one car, but they only broke away on right hand turns.  I see that Bachman has many couplers available. 

What do you suggest?  The couplers are the standard ones.  They came with set when shipped.