whats up guys, after a long year of ownership and two fresh engine rebuilds i am having a problem with warm starts only. cold starts the boat fires up immedatley and rungs like a top. We went out for a cruise, came back to dock and let it sit for an hour. it needed around 30 percent throttle to fire off but then slowly come back to idle and its fine. BOTH engines do the same thing. I did buy this boat from a owner that purchase from an auction. other then this issue it runs flawlessly now. its MEFI 3.

Injectors been serviced at any point? Leaky injectors will cause difficult hot starts but no problem at a cold start.
Also could be vapor locking if engine compartment is hot when you shutdown. Ethanol fuel will make this worse.

I had all 16 injectors professionally cleaned about 6 months ago but no run time on them since. what is there to do to prevent vapor locking if that is the case? would older fuel cause an issue? this tank is botched with 6 year old fuel and 1 year fuel with 10 gallons of new fuel lol

6 yr old fuel ?

20 gallons of it was yes, it was totally my fault. forgot to empy tank and then filled it. ill be draining it all and installing new filters this weekend

Well that's certainly a good place to start before doing any other troubleshooting.

I have twin 350s, 2001, MEFI 3 as well.
I did new fuel pumps, coolers, and pressure regulators. Solved a lot of my similar issues. it's a hassle to get all that off in the hull, so I just did 'all the parts'. The pump would work when it wanted to, and the pressure regulator was all rusted up.

Another cheap and easy experiment is to open the hatch when you shut it off, letting out the heat and see if that makes the situation better.

If it was vapor lock, it would sputter and would not want to stay running for the first 10-20 seconds after it fired up

Well im pretty confident i found my issue, ill attach a picture below. the right two where front the filters on the boat. the left is fresh 93. the right two bottles hardly had a fuel smell and when pumped into a drum is a dark brown. the fresh 93 has a very strong smell. much more yellow. Now thinking back i never had an issue with hot starts when it was running on the engine stand on fresh fuel. this would make complete sense