Just finished winterizing our boat. What a blast!

Hopefully someone can diagnosis my problem I've been dealing with all year. The problem occurs when initially starting the boat after it has been sitting for a while (cold). Boat starts up pretty quick, revs up and returns to idle. After idling for a second or two the engine just dies. Upon restart the engine will rev up a little (not as much as the first time) and return to idle where it will stay without stalling. Occationally the engine stalls when returning to idle from a higher rpm (~ 1200-2000 rpm). Replacing the spark plugs, cap, and rotor has helped somewhat with stalling when returning to idle from a higher rpm, but not for the initial startup issue. Any suggestions on what to consider?
Thanks for the help in advance.
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Thanks,
Ben
1998 258 Vista 7.4Gi Duoprop
