Yamaha F80 B - VST draining without press the valve

[RaduGabriel]

Hello.

First, I wanna thank you for allowing me to become a member of this group.

My problem: I just wanted to drain the VST. The motor is a F80 B 2007 Yamaha. Last time when I did it I had to push the valve from the top of the VST in order to allow the fuel to flow.

This time it was not the case. The VST was drained without pushing the Schrader valve. I just unscrewed the screw from the bottom of the VST.

Question: is it normal? Do I have to worry about it? I have no visible air leak in the system.

Thank you in advance for your advice.

[pstephens46]

If the motor runs well at all rpm don't worry about it.

[99yam40]

something is different, has to be getting vented to let the fuel out.

maybe Rodbolt could say what else could cause this

[RaduGabriel]

If the motor runs well at all rpm don't worry about it.

The problem is that it doesn't run quite well. I noticed power loss somewhere between 4000-4300rpm while I was trying to get the boat out of the hole, a power loss combined with a very low vibration from the engine. It was like a fuel or air starvation.

[TownsendsFJR1300]

My F150 VST will drain JUST loosening the screw...

Did you find any crap come out of the VST?

Is the fuel fresh or treated?

Can you get to WOT?

When it acts up, have a helper squeeze the primer bulb and see if that helps...

[RaduGabriel]

Yes, it seems something is different indeed.

-I've lost 200 rpm at WOT.
-in idle, the water separator is half full. It tries to get full when I accelerate but it does not become completely full. If I use the bulb I can get it full.

What I did: I changed the filters, primary fuel pump, the fuel line between fuel tank and engine, I cleared the fuel tank.

Any suggestions?

[fairdeal]

Yes, it seems something is different indeed.

-I've lost 200 rpm at WOT.
-in idle, the water separator is half full. It tries to get full when I accelerate but it does not become completely full. If I use the bulb I can get it full.

a visibly "half full" filter bowl is absolutely normal.

seems a 200 rpm loss may be tough to troubleshoot....

[99yam40]

Maybe see if rail pressure is staying in spec and have the injectors flow tested and cleaned.

Hope Rodbolt will comment on the VST being able to drain without having to press the shrader valve to let air in

maybe a relief /check valve not seating properly

[rodbolt17]

not the first time I ever saw the tank drain without using the tank mounted valve.
typically it indicates a low fuel level in the VST.
me I would worry more about the running issue.
the primary cup on the engine will stay about half full when running.
shot that wabbit for ya .

[RaduGabriel]

Hello again and thank you for your advices.

I solved the problem with the half full water separator filter. I opened the vent screw from the VST to drain the VST. After the VST was completely drained I left the vent screw in open position and I pumped fuel with the primary bulb until the fuel reached the VST and flowed through the draining little hose. I continued this operation until no more air was present in the fuel line and I screwed up the vent screw to close the VST. After closing the vent screw I continued to use the primary bulb until it was hard.

After a two hours trip on Danube river and half hour at idle the water separator filter was still full with no air in it.

Question: when the fuel fills the VST where does all the air from the VST go? Is there a valve or something?

Regarding the loss of 200-300 rpm at WOT I checked the timing belt and I had a suprise: it is quite extensible. When the engine is off the TDC mark was somehow aligned with the other two marks from the crankshaft wheels but when I tried to rotate the engine manually it was obvious that the timing belt was too extensible, such that the two crankshaft wheels started to rotate only when the TDC mark from the flywheel reached -5 degree BTDC. Trying to tension the timing belt was not an option since this operation was increasing the delay between the three marks. From what I saw, the delay is about 2/3 of tooth.

The timing belt is 10 years old, it was never replaced, so I ordered one today. It looks pretty good with no missing teeth. Perhaps it is the cause for a light idle vibration since the injectors are clean.

[RaduGabriel]

Thank you for your explanation.

What about number 16 (vapor shut off valve)? Where is it located? From what I see at my engine, there is only a hose between the charcoal canister and the intake manifold through ISC. Is this vapor shut off valve located inside the canister?

[rodbolt17]

ohhh I love mcrookies.

I cannot wait for you to watch that filter cup while running. they all tend to run about 1/2 full.
my F150 does, fairdeals does the guy across the canals does. as it is on the suction side it simply cannot remain full.

[RaduGabriel]

What is the complete identity of your motor? We don't have an EFI F80 here in the US.

F80 B is the european version of F75, same as european F100 D is actually the F90 from the US market. They are identical except the ECU and air silencer.

Rodbolt, I was concerned since, when it was new, my motor was running with the water separator filter full. I've thought the presence of the air in that filter might restrict the fuel to reach the VST in the correct amount.

You said that the fuel level in VST might be low. Do you know what the cause might be? The low pressure pump was rebuilt last winter, not because it was damaged but for my own peace of mind. After all, my engine is 10 years old and since I run it on Danube river I try to maintain it in good condition. I don't want to remain in the middle of the river with two big cargo ships navigating directly to me. The flow of the river is quite powerful in my region.