Yamaha F40 EFI will not run once warmed up.

[panasonic]

Those of us that are mentally ill enjoy these types of exercises.

Boat ownership....

Then we can tell the wife how much money we have saved.

I just spent $137 on diaphragms and orings for low pressure pumps that are working perfectly. But they are 12 years old.

That's called "preventative" maintenance. As opposed to "crap I am broke down, now how am I going to get myself ashore" maintenance...lol

[rodbolt17]

I had an F50 last summer that had similar issues. the fuel cooler was slam clogged. so bad I had to cut a piece of control cable inner wire,flatten one end with a hammer and chuck in in a drill and drill the stuff out.\

[Barney S]

Just some wild speculation on my part but it could be a valve that is not closing when the motor is turned off, thereby allowing excessive gasoline fumes to enter the air intake system. Having the cover removed could be allowing those fumes, if present to dissipate sooner than they might with the cowling installed.

If the old problem rears its ugly head when the cowling is left on, let us know. We can then tell you what valve to check to see if it is open or closed. Off or on in Yamaha's vernacular.

Put the covers and cowling back on and the problem is back. While it was messing up I removed the cowling and covers and let it air out real good. It still would not run. I drained the VST again with no help. I decided to do something against my better judgment and poured a large bucket of water over the intake side and fuel components. It would not fire at all for about 5 minutes then it started and ran perfect.

[boscoe99]

As rodnut suggests, inspect the fuel cooler to verify that gasoline can flow freely through its side and that cooling water can flow freely though its side.

One other test is to open the throttle about half way with the motor in neutral. Then proceed to crank the motor. Does it start up any quicker? Be prepared to quickly retard the throttle when it starts so as to not let the motor over speed.

I am thinking that excess fuel vapors are getting into the intake system causing the motor not to fire. Just a guess. Could be combination of excessive gasoline temperature in the VST. Does the VST feel hot after the motor has been running at idle for a period of time?

[rodbolt17]

if you suspect the VST vent is leaking(it is ECU con*****ed) simply when you stop,unplug it and see,
fairly simple.
even with the fuel cooler slam plugged the tell tale works on that model.

[pstephens46]

Unhooking vent line before shutdown mentioned before. So this makes three times. Or just keep riding around....