Hello Longmill,
Lets get a few things answered.
First, have you checked the idle setting? without the airfilter on, you should be able to look down into the carburator and see a 1mm opening when at idle.When you apply your brakes, that should never fully close. it should just limit the fuel enough to keep the engine running .
Second is the glow plug. Have you checked to see it glows bright?
Last...what is "broken in"?
Please give us some answers to help you out.