Did a job today, turned the vacs on but forgot to put cap on waste pipe so machine starting wobbling abit with water full. Started up again then minute later the whir of motors started to whine down then thers smoke coming out

, I thort thats it, but waited a minute, turned them on and they worked fine for rest of job.
Was it another intake of water or what? Are the chinese motors supposed to be cheap because i've got two in mine.