2004 Yamaha F-225 Fuel leak when tilted

[fishhawaii]

OK I see there have been other threads that touch on this a little but I need all the help I can get with this one.
A week ago, after a day of fishing and putting the boat on the trailer (engine tilted full up) I noticed a strong fuel smell with a large quantity of fuel dripping out of the front of the cowl below the plastic fuel filter. It was raining so I just trailer-ed home. By the time I got there there was little smell and fuel had stopped dripping. The next day I removed the cowl and squeezed the ball. No leaks , no fuel smell, engine was dry. Ran the engine in a bag for a good 1/2 hour no leaks or fumes noted.
Concerned about fire, I called my mechanic friend and he told me to bring it over. Once there we took off top plastic cover (to inspect hoses on top of motor) and ran the engine for an hour, No leaks no fumes. Took the boat home (after tilting the engine up again and no fumes no leaks.
Later that afternoon took the boat for a ride and engine purred. Stars right up. Smooth running and 6100 RPM convinced me the problem was somehow gone. Pulled back to the ramp and as soon as the engine was tilted up a large sheen of fuel was seen behind the boat. i reached down and the raw fuel running out of the forward part of the engine filled my hand twice. Unfortunately right then it started raining very hard and it was impossible to remove the cowl. Got home the next morning and no residual fuel, no fumes, no leaks. pressurized the filter by squeezing the ball, with the lift pump running, tilted the engine. No leaks no smell, ran the engine again and seems to start and run fine. Tomorrow I plan to run it on the water and repeat the previous steps but tilting the engine with the cowl off and flashlights in hand.

I do swear that both times this happened there seemed to be a small amount of oil in the splashwell too. Something I have never seen. Oil level is normal and no fuel there.
One more question is there a drain hole in the front of the engine? I see none so I;m wondering how the fuel in coming out without a puddle of residual somewhere in the front. Maybe another question is there a check valve in the system that could stop fuel from draining out of the air intake? if anything it seems like a slight fuel smell is coming from behind the plastic air cover on the front of the engine but very minimal.
Any ideas or help would be greatly appreciated.

[TownsendsFJR1300]

I'd look very closely (at least pull the clear filter section off) at the under cowl fuel filter. There's also a gasket under that cup:

2004 F225TURC Yamaha Outboard FUEL 1 Diagram and Parts

A high pressure line with a hairline crack, etc would be suspect.

As you noted, if you can't find this while stationary it may need to be checked while under-way as its only happening at much higher RPM's. Shouldn't be hard to find once it starts leaking...

If you get the tool (forgot the name) in place of the prop, to put the load on the engine with higher RPM's while stationary would be MUCH SAFER.

If not, I would run with the main cowl off (as much as its leaking it'll still show) and a helper to drive or watch with a fire extinguisher.

As for any oil too, the fuel is likely just washing down the engine every time it leaks the large amount.

Good luck and please post back.

[fairdeal]

i reached down and the raw fuel running out of the forward part of the engine filled my hand twice.

Makes my hair stand on end.

I can't think of why "high rpm operation" would cause more leakage than running at a lower speed...

but then,

I've never understood why the SM says the fuel rail pressure should "increase gradually" to 44 psi during the 5 seconds the HP pump runs at key on, but then drops to 38 psi at idle

Regardless, I would be going over every inch of fuel-carrying hose, and every connection,
from where it enters the cowling right through the VST, fuel rails, cooler, vents and carbon canister.

(I recall Capt. Solo posted a while back of his cowling blowing off due to a linking joint on the fuel rail hose...)

[fishhawaii]

Thanks Guys still no luck. To make matters worse it now only leaks out sometimes. The other day no leak noted until I got the boat home. Is there a check valve on this engine that could cause this? help is greatly appreciated.

[boscoe99]

I've never understood why the SM says the fuel rail pressure should "increase gradually" to 44 psi during the 5 seconds the HP pump runs at key on, but then drops to 38 psi at idle

The fuel pressure is tied to the intake manifold pressure. There is a sense line that runs from the regulator to the manifold.

Before the motor is started the intake manifold pressure is as high as it ever will be. So, when the key is turned on the fuel rail pressure is as high as it is supposed to ever be.

When the motor is started the intake manifold pressure drops. The regulator senses this drop and decreases the fuel pressure accordingly. As the intake pressure rises and lowers with the throttle opening and the change in engine speed the fuel pressure will be going up and down as well.

Read the section on Fuel Pressure Control. You seem to like to read and want to know more about this stuff. Good for you.

HOW ELECTRONIC FUEL INJECTION WORKS

[boscoe99]

Thanks Guys still no luck. To make matters worse it now only leaks out sometimes. The other day no leak noted until I got the boat home. Is there a check valve on this engine that could cause this? help is greatly appreciated.

No check valve that should be allowing fuel to come out of the system.

If that were my motor I would run it without the cowling on for a period of time while carefully inspecting all of the fuel system components. Intermittent problems are some of the most difficult to find. Keep looking. Fuel leaking is not something to be played with.

If you need a diagram for the fuel system to help you check all of the components just holler.

[fairdeal]

The fuel pressure is tied to the intake manifold pressure. There is a sense line that runs from the regulator to the manifold.

Before the motor is started the intake manifold pressure is as high as it ever will be. So, when the key is turned on the fuel rail pressure is as high as it is supposed to ever be.

When the motor is started the intake manifold pressure drops. The regulator senses this drop and decreases the fuel pressure accordingly. As the intake pressure rises and lowers with the throttle opening and the change in engine speed the fuel pressure will be going up and down as well.

ahh yes. Actually on my six-throttle-body F225, a spaghetti bowl's worth of tubing.

I think first of the electronic controls, forgot that there is a mechanical element as well.

Informative link - thank you!

[fishhawaii]

Thanks guys,
I spoke to a mechanic and we think that the fuel is coming out of the airbox after the engine is shut down. it makes sense as their is no residual fuel or fumes in the cowl. I'll spend some time reading the info and looking at the fuel schematic. Thank you for the info its greatly appreciated. Any knowledge of the VST needle or check valve causing raw fuel to come out of the airbox? It just might be a small leak that collects fuel there until the engine is tilted too.
Going to see if w can run it with the airbox off and loo around. Thanks again!

[fairdeal]

of course the VST has to be able to vent air/fuel vapor, and it does that to the top of the intake silencer -

so are you getting liquid gasoline exiting the VST through the vent?



interesting, particularly since it seems you are seeing this happen when the engine is tilted,

which of course changes the orientation of the VST and the fuel level in it.....



but what about your engine has changed from "normal" to cause this problem?


is the fuel level in your VST "too high" due to a leaking needle valve?


or there's that inline "Orifice, air vent"

(which I've "examined" in the past, without coming to any understanding of what I was looking at)

it didn't seem to have any "moving part" (no spring loaded ball) - just seemed to be a "flow restrictor".

The only "failure mode" I would imagine for it, would be to "plug", not "fail open"....



Then the other aspect I find mysterious: there are TWO vent ports on the cover of the VST - why isn't one enough ?

[fishhawaii]

Thanks Boscoe and fairdeal for your replies. I have ordered the VST Gasket and a new needle valve. Should be here in a few days. Then hopefully my mechanic will take apart the VST and we can clean it out. It had problems with screen clogging about 500 hrs ago. We are planning to inspect that return line on the cover too. Any other ideas to help avoid a fire will be greatly appreciated.

[fishhawaii]

By the way engine purrs, starts and runs like a champ 6100 RPM but now I think every once in awhile at higher RPM, I think I hear a very subtle pop or backfire. Like a slight miss. Maybe the problem will begin to show itself now.