2013 Mercury pro xs 200hp. Running rough

I have a 2013 legend with a 200hp Mercury pro xs. I just had a new power head installed. Now it has approximately 23 hours on it. I recently had it in the shop due to it running rough and would die. The shop replaced the air diaghram and found that the fuel pump (high psi) was installed backwards. I also had them replace all my spark plugs and perform a service on my lower unit. I finally got it back and now it runs rough on first initial start up for a couple minutes and occasionally dies if i do not give it alittle throttle. After a few minutes it will finally smoothe out and run great at low idle or WOT. If I turn the engine off and it sits for a a couple minutes the problem comes back when starting the engine. Please help!!!!

What happened to old powerhead?

faztbullet said:

What happened to old powerhead?

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The boat was sitting under my car port and at the time I did not cave a cal cover. Long story short a dirt dobber got in there made a nest in the air intake and It sucked it up into the engine and dusted it.

Put a fuel pressure gauge on the rail run the engine and shut it down. How long for the pressure to drop to zero?