2014 F90 hard to start when engine is hot

[sthomasIV]

2014 F90 on a g3 1860cc so it is a yamaha factory rig that is system matched. Little over 50 hrs. Serial number 61PL1069740. Has done this since new but only in warmer months of the year. Will start fine and run fine. Turn off and immediately restart, does fine. Turn off and fish a spot (10-15 minutes or more) and it takes 2-5 attempts to get it to stay running. Ususally it will run for a split second and shake then cut off (acts like it is vapor locked or starving for fuel). Pumping the bulb makes it worse. First dealer adjusted float in VST and checked the canister hoses and fuel pump. This didnt help. Was told to switch were i bought gas (up untill then only nonethanol from one store). I have tried all types of fuel since with same results. That dealer went out of business so earlier this summer took to different dealer. They checked fuel, fuel pump and numerous other things. They ended up calling yamaha and yamaha had record of my ongoing problem and said to replace the entire VST. Thought sure this would cure it but the same or actually worse now. Supposedly, Yamaha told them they would send another VST since that one didnt fix it? Is there a known issue with these VST's that Yamaha would be willing to send out another one so easily? Any help would be appreciated as i fear due to lack of yamaha techs in my immediate area i may never get this figured out. I have tried removing the gas cap on the boat to insure its not a gas tank pressure issue with these new EPA mandated gas tanks. This boat has a 20 gallon built in tank and takes gas just like a car at the pump with no spewing or kick back. I have also tried running the engine without the cowl and it does perfect when starting. (Last time out it started doing the hard start issue and removing the cowl cured it, replaced the cowl and it started doing it again). Again, it will do this consistently in the summer time. It must sit for at least 10-15 minutes after operating. I have plenty of videos of what it does that i have shown both dealers. Thanks again.

[panasonic]

Any rub marks or signs of chafing on the inside of the cowling? Meaning when the cowl is on it is pushing against the wiring harness somewhere...

[rodbolt17]

my guess would be to check the VST vapor shutoff valve.
it is not part of the VST.

[fairdeal]

yamaha had record of my ongoing problem and said to replace the entire VST.

Yamaha told them they would send another VST since that one didn't fix it?

talk about throwing parts. Can't say Yamaha doesn't provide warranty coverage.

Rodbolt's diagnosis is that you are not "vapor locked or starving for fuel"
but rather too much fuel - "flooded"
Not that terminology helps your problem, but until you get it fixed,
ii may help in those situations to press the release button and advance the throttle before cranking, to give the engine "more air"

the VST is supposed to vent fuel vapor - allow that into the intake -
but there's a carbon canister system, designed to do that on a con*****ed basis

[sthomasIV]

Just checked and no rub marks on inside of cowling. All wiring harnesses look brand new and not chaffed.

[sthomasIV]

my guess would be to check the VST vapor shutoff valve.
it is not part of the VST.

Thanks guys! Really appreciate all the help so far. Is that the check valve right after the fuel pump that goes to the VST? If so just take it off and test by blowing air both ways? One way lets air thru the other won't?

[rodbolt17]

our EPA regulations do no allow venting of fuel vapors to the atmosphere.
so they use an electric valve and the ECU to vent the VST.
any vapors are held until the engine starts then the valve is slowly opened to vent the vapors to the intake and be burned.

if the system leaks it creates an over rich fuel/air mix in the intake and makes hot restarts difficult.

a clogged fuel cooler will do the same.

[sthomasIV]

talk about throwing parts. Can't say Yamaha doesn't provide warranty coverage.

Rodbolt's diagnosis is that you are not "vapor locked or starving for fuel"
but rather too much fuel - "flooded"
Not that terminology helps your problem, but until you get it fixed,
ii may help in those situations to press the release button and advance the throttle before cranking, to give the engine "more air"

the VST is supposed to vent fuel vapor - allow that into the intake -
but there's a carbon canister system, designed to do that on a con*****ed basis

both of you guys know exactly what I'm talking about when i say its starving for fuel or vapor locked. The way it runs for a second or two and then shakes (sometimes a lot) then cuts off would lead you to think it is not getting fuel but the fact that pumping the bubble makes it worse has verified to me it is getting too much fuel or fuel vapors. Also performs fine in winter or cooler months............removing the cowl proved that as well................right after VST replacement spent 6 hours on the water fooling with it................did it 6-8 times in a row consistently then removed the cowl during the hottest part of the day and it did fine.............replaced cowl and it did it like 4-5 more times in a row. I have faith now that i can get this figured out this summer with you guys help. Love yamahas (3rd one) but lack of techs or master techs in my area are slim. Rodbolt might be the closest in KDH. Thanks again!

[sthomasIV]

our EPA regulations do no allow venting of fuel vapors to the atmosphere.
so they use an electric valve and the ECU to vent the VST.
any vapors are held until the engine starts then the valve is slowly opened to vent the vapors to the intake and be burned.

if the system leaks it creates an over rich fuel/air mix in the intake and makes hot restarts difficult.

a clogged fuel cooler will do the same.

was told by dealer when they replaced the VST that i got "everything new after the fuel pump to the canister" which should have included the fuel cooler i presume? So can i test the vent you speak of or do i need to let my dealer check it?

[sthomasIV]

Thanks guys! Really appreciate all the help so far. Is that the check valve right after the fuel pump that goes to the VST? If so just take it off and test by blowing air both ways? One way lets air thru the other won't?

Just checked yamaha parts diagram and what i thought could be the vapor shutoff valve is actually part #19 a Strainer. Do not see a vapor shutoff valve in parts breakdown of either fuel injection pump 1 or 2 online?***Edit**** just found it i think..........Part number 10 under intake 1 section. Black with a horn sticking out the side. How do you test it?

[Aliboats]

Some silly questions ..
Have you replaced the secondry fuel filter (69j-24502-00) not the element inside the see thru filter housing, there is another.

Are you running with some sort of cowling protector or hood over the cowling ? material cover ? are the air intakes restricted for what ever reason ? (even very thin gauze type material can really choke a motor)

Have you replaced the ISC valave ?
When you shut down the motor after a good run, do you hear the ISC valve operating and some clicking sounds ?
Have you done a quick test with the ISC valve unplugged ?

[sthomasIV]

I have not replaced any fuel filters, last dealer checked all that before yamaha would send the VST. They must have thought I had bad fuel or a bad fuel system. Tech said my fuel and fuel system was perfect..........."clean as a whistle" Always had used non ethanol but switched brands and have tried everything including ethanol after 1st dealer told me to buy some different fuel. Always run ring free in every drop of gas. No cowling protectors while running (I do have a yamaha cowl cover that i use if the boat sits out overnight but never operate with it on) No restrictions in cowling (I checked that when I figured out with cowling off the motor was fine)
I have not replaced the ISC valve (when the cowling was off the other day while testing i could hear it clicking fine at shutdown)

[rodbolt17]

just cause it clicks does not mean it physically moved.
may need to clean/lubricate it.
I use Yamaha combustion chamber cleaner.
sounds like an issue of to much fuel to not enough air.

[sthomasIV]

just cause it clicks does not mean it physically moved.
may need to clean/lubricate it.
I use Yamaha combustion chamber cleaner.
sounds like an issue of to much fuel to not enough air.

Ok I admit upfront i am not a Yamaha mechanic and am an idiot to you guys that know these engines forwards and backwards..............but now I am confused as well...................Is the ISC, IAC and VST vapor shutoff valve the same part? Reason being i have found what i think is the VST vapor shutoff valve (Part number 10 under intake 1 section) which seems to be by reading another thread on here what some say is the ISC/IAC. Help!! I am now not just an idiot but a confused idiot. Gonna take to the lake today and test some things if I can.................What can I do to test/eliminate some things?

[boscoe99]

talk about throwing parts. Can't say Yamaha doesn't provide warranty coverage.

The Yamaha guy is sitting at a desk in an office hundreds if not thousands of miles from the mechanic and the motor. He may or may not be an actual mechanic. If he is, he may or may not have actual experience with the F90. If he has experience with the F90 he may or may not have dealt with a similar or identical problem on the F90.

It is the job of the actual mechanic in the field to find and fix the problem. Yes, it can be difficult and frustrating. The mechanic in the field calls Yamaha for help. All the guy behind the desk can do is to throw some suggestions to the mechanic. What else can he do. He wants to help. Some good, some bad, some ugly ideas. Kinda like what is done here. If the gods are looking down and smiling the two may stumble upon a fix.

If the mechanic is not too proud to ask for help (real men don't ask for directions) he can ask for an actual Yamaha mechanic to come to the shop and help him find and fix the problem. My experience indicates to me that lots of mechanics today are parts changers. They have little theoretical knowledge regarding how the stuff all works together. They want a computer to tell them what is broken and what part needs to be fixed. This is how an overly rich condition gets referred to as "vapor" lock. They might be thinking that too many fuel vapors are locking the motor from starting.