Throttle needed to start

First I would say hi, I've been lurking off and on for the past year or so. Bunch of great looking rides!
Anyways here is my question. I have a 1982 Ski Nautique with around 570hrs. The engine is a 351 and starts up fine here in the drive way with just a bump of the key. (no back pressure?) Now out on the water it's a different story. She will run perfect but once you turn off the key, I have to give it neutral warm up throttle every time I want to start her otherwise it takes 10-15 sec of cranking for it to start. I don't know if this has anything to do with it but what I have noticed it that engine temp goes from 160 degrees while running to 220-230 while off then back to 160 once it starts. Normal heat soak?(has new impeller) Carb has been rebuilt but I'm guessing that it may need tweaking?

Bri892001 wrote: Hmmm, a little more info. Are you saying it starts easily when cold (on the trailer) but in the water (hot? assuming you're running it) it's harder to start?

Correct to both

Good ideas above. One more suggestion too, make sure your choke plate is opening up as it should. It should be totally vertical when the engine is warm.