Stall problems when starting Volvo 5.0 GXI SX Outdrive

[Rick Cavallaro]

I have a 2003 Hurricane deck boat with a 5.0 GXI SX outdrive Volvo with about 390 hours. Occasionally at start up it is necessary to disengage the gears and advance the throttle to 800-1000 rpm to start the motor (fuel injected). When returning to idle the motor will stall below 500 rpm. When this happens is not possible to engage the gears and therefore not possible to run the boat. This more frequently but not always happens when the motor is hot, turned off (fish, swim) and then try to restart. It was originally diagnosed (guessed) as a vapor lock in the fuel line. No correction was made. It less frequently happens with a cold motor. Later in the day or the next day the motor will start perfectly at idle and operate normally.

Any one experience anything similar? Any suggestions?