Mercury Outboard EFI bog and die?

Question

I have a 1995 200HP Mercury Outboard EFI 2.5L with a newer 2004 powerhead. It has a hard time starting without being given some throttle (in neutral lockout). It runs for a few minutes and then bogs down and dies (not under load, in neutral). Seems to bog even more if you give it throttle. Then it will not start again until it fully cools off. I just ran it about 20 miles a week ago and it ran just fine. But started exhibiting this (staying running) problem after coming back to it after a couple of days. The hard start (requiring some throttle) has been an issue for a long time; however it ran OK otherwise before.

Does anyone have any insight on what would require me to give an EFI throttle to start and why it would bog down and die? I can't help but feel the 2 problems are related.

I've tested the vapor separator, fuel pressure regulator, electric fuel pump and fuel delivery seems OK. It has new spark plugs.

Answer 1

First off (which I am sure you know) you should never have to start an EFI with throttle... they should be starting on their own.  It is actually a big NO NO to even try to do that.  I would have 2 guesses here:

1) you need to replace all fuel lines - boat fuel lines are double   lines - so there is a small line inside of a larger line.  When they get old the inner line can break away from the outer line.  The inner line is thin a and when it breaks away, and you throttle the engine, the engine will try to start really sucking gas, but will instead suck the inner line so hard it closes on itself.

This would explain the bog down when throttling, and it could explain the starting I guess, if the line is so bad it is already partially closed, giving it gas could get a little fuel flowing to it to get it started... at idle the engine is not sucking fuel very hard, so it should idle, but once you power up it would close.

2) I am not sure about the Merc's (I know the Yamaha's have them) there are tiny fuel filters that are directly at the injectors, if they get clogged at all, or need to be replaced they would restrict fuel flow, and when you throttle up would not give the engine enough fuel