Couplers on McKinley Explorer

[Grampa Terry]

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.

[SteamGene]

First question is:  Are they horn hook or knuckle? 
Second question is: If knuckle, are they the older Bachmann knuckle with a plastic spring or the new ones with a metal one. 
Third question is:  If they are knuckle and you don't have a coupler heigh gauge, have you gotten down to eye level with the couplers and insured they are level with each other?
Gene

[Grampa Terry]

#1.  They are the knuckle couplers. 

#2.  I do not know if they are the older Bachmann coupler.  Is there a way to check this out? 

#3.  No, I do not have a coupler height guage and I did get down to eye level when this happened.  One car would stay hooked up to the engine, but the others would break away.   Also, this was on a flat surface - no slope.  I did notice that when I checked the height of the coupler connection, the engine coupler wanted to raise up over the cars coupler.

Thanks