Fuel starvation yamaha f225

[marchmadness]

Since Im loosing sleep thinking what im doing wrong I forgot to mention with the motor vented directly when I started after being warm I did have some fuel come from the vent . There was a long thread on the hull truth where a lot of others have or had the same issue. They kept on calling a vapor lock .

[99yam40]

If the vent is on the top of VST, how would liquid fuel get up that high?

float not shutting off the needle when VST was full is the only reason I could come up with

[marchmadness]

Not sure but I think it has to do with pressure. Nothing leaking when sitting . I replaced the needle valve and it was opening closing. Also I direct vented the other motor and it did the same. Again this only happens when HOT...

[marchmadness]

Yes I’m still on it . And yes my good motor is starting to get the same systems. Yesterday I hooked in a plastic tube before the filter. It appears that the fuel drains back when the pump starts it’s cycle. Is it supposed to stay full?

[marchmadness]

[99yam40]

pump sucking air maybe

[panasonic]

I believe Rodnut mentioned and/or I read about an anti siphon valve in the system before the fuel pump.

Not 100% on that location...but would make sense to me that this valve (check valve) would prevent the fuel from being siphoned back towards the fuel tank when fuel pump is off....

Again this is just from memory, so check your SM to see if this actually part of the system on your engine. I don't want you to go chasin ghosts...

[rodbolt17]

the anti-siphon valve,if equipped,will be located on the fuel tank draw tube.
it can act as a check valve but that is not what it is designed for.
the check valve in the fuel primer bulb should stop some of the fall back but that is normal.
that is why the pump runs 10 seconds.
I still don't think the vst's are staying full.

[marchmadness]

I hooked air pressure up before the fill cup and put the system under pressure looking for any leaks. So I’m still at square one but know my good motor is acting up. Not sure what to do next

[99yam40]

Yes I’m still on it . And yes my good motor is starting to get the same systems. Yesterday I hooked in a plastic tube before the filter. It appears that the fuel drains back when the pump starts it’s cycle. Is it supposed to stay full?

do you mean when the pump turns off?
or when it turns on?
starting a cycle to me means start up and then turning off

[marchmadness]

The hose filled when the pump came on and went empty off

[rodbolt17]

I will try to slpain this one mo time.
the fuel delivery system on this F225 is like this.
a lift pump supplies the VST with fuel.
lift pump below 1200 RPM cycles at ten seconds on 20 seconds off.
the output of the lift pump fills the VST until the needle valve in the vst shuts.
if the lift pump is still on when the needle shuts the excess output is routed through a relief valve that opens at 10 psi back to the lift pump intake.
if there are any air leaks in the pump intake OR the relief valve leaks it starts introducing air into the lift pump intake.
now the VST starts running low.
so when your idling while setting ancor or whatever then you restart and idle while getting ready to get underway the VST is using fuel but not receiving fuel.
then whammo you nail it to get rolling.
about 60-100 yards into it uuuggghhhh.
vst is out o gas , nothing for the HP pump to supply the injectors.
motor dies.
the VST and high pressure system is working.
the lift pump works.
find the air leak or fuel restriction between the lift pump intake and the liquid level in the tank.

[marchmadness]

Rodbolt thanks for being patient with me. So you would suspect that the vst never fills? when im running it is always playing catchup ? Then if I was at your shop, and I wish I was, where would you start looking? These motors are equipped with fuel monitors could that be a source of restriction? I guess what's throwing me off is that this only occurs after shutdown.

[TownsendsFJR1300]

The VST is filling however once stopped, the fuel in the system (hoses, primer bulb, etc), is RUNNING BACK OUT to the fuel tank.

The engine starts and runs on what's LEFT in the VST for a couple of minutes. Then, with the fuel in the lines DRAINING, you have air in the system, there is NO fuel.


Do you have a fuel / water separator? Have you checked the sealing surface / o-ring gasket there? As noted earlier, the primer bulb should help keep fuel from flowing back into the tank..

[marchmadness]

I have a fuel separator on each motor and fuel monitors . All are original to my 03 boat . unless I hear different I was going to start at the tank and replace all to the motor filter including the cup and gasket. I was thinking of by passing the fuel monitors?