Put it together without screws, make sure the lugs on the motor unit are in the slots on the shell and that the wires aren't trapped between the motor unit and the shell, I tape the wires on mine under the lip on the tray.
yep i make sure of that. and so do i.
Do the shells actuall meet properly down the middle or is there a gap? Does it run ok with the shells on but not screwed?
there is a gap at the feed neck part of the shells and when pushed together to meet, thats when the motor really struggles.
If there is no gap. Put the screws in but don't tighten them fully, does it run witht he screws a bit loose? If it does then tighten each screw fully one at a time to see which screw is causing the problem.
i have no screws at the moment
It's a bit of a process of elimination