Hi Ching,
My motor have below problems:

90hp, Evinrude/Ficht, 2 stroke/4cyl.

The motor starts and idles ok, but after warming it up for a few minutes, it will die as soon as it's put into gear. I would think after being tuned up it should run ok without dying. The new plugs were pulled and rechecked, one was found to be broken, and the other 3 oil fouled. All 4 were replaced, and the dealer says they can't find anything wrong with it, but it still dies as soon as it's put into gear. After repeated attempts it will finally stay running, but when we do get it moving it will not get over 3500 rpm's, according to the tach. The previous owner claimed it ran fine for him last year. Any ideas what could be wrong?

one plug was found to be broken?

u better check the compressing pressure to make sure that cylinder stays fine

if it is and tune up the idle rpm