I just wanted to add to this topic and state that, despite the recent updates to both BeamNG and Automation within the last week or so, this issue STILL exists.
I have a thread of my own I just started for the same problem…smaller engines instantly ‘locking up’ in BeamNG when you start to accelerate away:
http://discourse.automationgame.com/t/engine-breaks-instantly-in-beamng-no-matter-what-car-i-put-it-in/34354
Quite frustrating as the same small engines always used to work fine in BeamNG/Automation about 2-3 updates ago, so something has changed. Hopefully the issue is still being worked on so it can be fixed! 