2003 21ft Rinker Captiva with 5.0 MPI w/alpha. Boat ran good in January at 500 ft elevation. Winterized and moved to 7500 ft in February. In June, pulled boat out and ran good w/muffs at the house. Went to the lake (6200 ft and about an hour and a half later) and the boat would start and die. Finally after about a half hour the boat came to life and ran fine the rest of the day. It was mid 90’s with water in the 60’s. Boat restarted fine (sat for an hour or so in between running).
Next trip: boat initially started/ran fine, starts and dies quickly after it has been sitting 15 minutes to an hour. Starts fine after a couple of hours of sitting. Does this all weekend. When it starts, it seems to run fine. It was in the 90’s during the day with water in the low 70’s.
Assuming that my problems were due to vapor lock, I changed the water separating fuel filter. Initially, I did not fill the fuel filter with gas, and the boat would not start. Removed fuel filter, added gas, and motor started and ran fine for about a minute and then sputtered out and would not restart. Checked fuel filter to find fuel level in the filter was down nearly an inch. Re-filled the filter with gas, and once again the motor ran for about a minute and died same as before. The fuel pump does run for 3-4 seconds when the ignition is turned to the run position. It sounds like it bogged down a bit when I filled the fuel filter. (The pump has always seemed to be inconsistent in pitch – tapers to a lower pitch while cycling.)
Where should I start?
Thanks

I'm having a similar problem with a 2006 350MPI. After I run the boat in hot and humid weather and stop and sit for a short period of time and try to restart it doesn't start until continually try to start it 15-30 times. If I sit for an hour and try to restart there doesn't seem to be any problems. I've changed the fuel filter and added fresh gas but still have the same problem. They boat has never sat outside or stayed in the water overnight so water in the fuel system shouldn't be the problem. I only use premium fuel in this boat also. I'm going to try and call a Merc Service Tech to see what they have to say about this problem. A friend of mine has a 05 305MPI and has experienced this same problem and called he a Mercury Service Rep and the Service Rep mentioned something about a higher pressure fuel pump. I'll take the boat in the shop next month to see if there is a fix for this starting problem and post it if it gets fixed.

add a low pressure merc pump to act as a primer to the high pressure have done this on many searays due to heat build up in engine compartment and lack of enough ventalation, in fl engine caopartments get up to 200degrees.