Hi HW ,
Take it you mean they are simply clamped down with nothing attached.
If that's the case it would seem you definitely have a pair of duff motors .
Think you need to be having a few serious words with mtronics
You might also think about getting a pair of 385 motors instead - much more torque with 5 poles - and unless its a speed boat work much better - but beware like the 400s there are some serious amp eating versions around - ask your supplier for advice and get a pair that will happily run on 7.2v.- ones rescued from better halves old hair dryers prefer 19 to 24v.........