F 115 fuel system issue

[captron904]

Thanks. I still haven't run on the portable tank yet. Hopefully this week.

[99yam40]

yep pumping the bulb until tight and then draining the VST will show how much should be in there, or maybe even under normal running condition.
and then right before a restart 30 to 60 minuets after a good run will tell if the VST is lower that it should be.
if the tech took pressures when the problem was not there, then it was a waste of his time.
need to be testing when the problem shows up to compare them.

[DennisG01]

I did not drain the VST tank right before I normally would have the problem. By doing that what would that tell me?

See post #6. It will tell us if the fuel that SHOULD still be in the VST tank is/isn't there. Sort of a "double check" thing

[captron904]

The fuel bulb is mounted in the vertical position.
Probably going to replace the low pressure fuel pump.
I did not drain the VST tank right before I normally would have the problem. By doing that what would that tell me?
I’m going to try the portable tank tomorrow to eliminate the boat side of the fuel supply.

[captron904]

"did you see water flow out of the lines, not just run a string into the lines? YES GOOD WATER FLOW

did you start the motor on muffs with the lines disconnected one at a time to make sure?
maybe hook a clear tubing in and out to see water flow? YES

seems like I have read about a problem before where the point the water flow went back to the motor to exit stopped up keeping flow restricted.

Has the problem showed back up yet? YES EVERYTIME ITS HOT OUTSIDE
Maybe the Yamaha tech cleared out a restriction when he was checking things out and it is fine now.

I fired up my C40tlrx last week for the 1st time in a couple of months since the winter showed up.
No water flow from my Tell Tail even when shoving along piece of weedwacker line up it several times while it was running at high idle on muffs.

yesterday I used compressed air to blow into the TT and then started the motor again while on muffs to make sure I really needed to take the lower off to inspect the water pump, and it has very good water flow now.

[99yam40]

how long can that motor run with just the VST full?
seems like some have written about idling fine but could not get up on plane?

But that could have been totally different motors

So the need to know if the VST is getting low and where that fuel is going.
could the bypass valve be sticking open recirculating fuel instead of putting it into the VST, causing the VST to be low on fuel?

Just guessing at stuff right now.

[DennisG01]

If the VST was getting that hot, I think it would be easy enough to tell just by putting your hand on it? It would have to get awful darn hot to get rid of that much fuel in a short period of time, right? Meaning, unless I'm misremembering, this issue can happen in as little as 30 or 60 minutes?

Captron, did you respond back about trying things with the hood off?

I waivered a bit on thinking it was supply issue... but I'm kinda coming back around to that.

[99yam40]

I would think if the liquid fuel vaporized from heat in the VST, it would need to be gone from the lift pump also to keep the lift pump from pumping new liquid fuel to the VST.
It is very hard for a pump to pump air out of the way.
that is why there is a primer bulb in most systems.

does the bulb feel like it does not have liquid fuel in it when you have to pump it?

If the bulb and lines/filters stay full, I would make real sure the fuel cooler is getting the water flow it needs

[DennisG01]

Dennis , I had to think a little to finally figure out what an AS valve was.
But it did finally come to me.

Sorry 'bout that!

For anyone else wondering about my abbreviation "code". AS = AntiSiphon valve.

Truthfully, I was just kinda thinking outloud there based on the fact that the bulb seemed to have gone flat (sort of) or at least that he said there was air in the fuel hose - which I assume he meant the portion of the fuel hose between the bulb and the tank.

[99yam40]

OK, let me explain one more time in detail. I use this boat pretty much every day. Recently, after launching the boat in the morning and moving from spot to spot. After the engine is off from anywhere from 30 minutes to an hour, it is starving for fuel when I crank it up. importantly, I can squeeze the ball to re-prime, the fuel line, and it starts fine after that and picks up fuel and everything is great until the next stop. It’s obviously more prevalent when it’s hot outside. We have pulled the coolant lines to the fuel cooler and an even ran string through it to make sure it was clear. Which it is. Running wide-open, idling, and everything else is perfect except for after it sits off for a short period of time when it’s hot outside.

did you see water flow out of the lines, not just run a string into the lines?
did you start the motor on muffs with the lines disconnected one at a time to make sure?
maybe hook a clear tubing in and out to see water flow?

seems like I have read about a problem before where the point the water flow went back to the motor to exit stopped up keeping flow restricted.

Has the problem showed back up yet?
Maybe the Yamaha tech cleared out a restriction when he was checking things out and it is fine now.

I fired up my C40tlrx last week for the 1st time in a couple of months since the winter showed up.
No water flow from my Tell Tail even when shoving along piece of weedwacker line up it several times while it was running at high idle on muffs.

yesterday I used compressed air to blow into the TT and then started the motor again while on muffs to make sure I really needed to take the lower off to inspect the water pump, and it has very good water flow now.

Dennis , I had to think a little to finally figure out what an AS valve was.
But it did finally come to me.

[DennisG01]

So... what if... the AS valve either isn't there or is stuck open... and the fuel bulb is mounted relatively horizontal instead of the recommended more "vertical" orientation. Could those two things cause a siphoning effect OUT of the VST tank?

Maybe an issue with the low pressure pump?

You didn't mention if you drained the VST tank right before you would normally start up and have the problem. Try that. How much came out?

Portable tank. It's still a good idea to do that to eliminate the entire boat side of the fuel supply.

[captron904]

The problem is starving for fuel at start up later in the day as it gets hot, or the engine gets hot. There’s obviously air in the fuel line as I squeeze the ball I could re-prime it in the edge. It goes from a rougher idle to normal in a couple seconds, after squeezing the primer ball.

[captron904]

OK, let me explain one more time in detail. I use this boat pretty much every day. Recently, after launching the boat in the morning and moving from spot to spot. After the engine is off from anywhere from 30 minutes to an hour, it is starving for fuel when I crank it up. importantly, I can squeeze the ball to re-prime, the fuel line, and it starts fine after that and picks up fuel and everything is great until the next stop. It’s obviously more prevalent when it’s hot outside. We’ve pulled the coolant lines to the fuel cooler and an even ran string through it to make sure it was clear. Which it is. Running wide-open, idling, and everything else is perfect except for after it sits off for a short period of time when it’s hot outside.

[99yam40]

Problem is more frequent when its hot outside. Once the engine cools down over night it starts and runs perfect until later in the day. Always runs great, but looses prime (air in fuel line) after engine is off 30 plus minutes, and is hard to start.

I thought you said, you can pump the primer bulb and it will start and run just fine after running and sitting for 30 minuets.

you still have no idea how much fuel is in the VST after you shut the hot motor down and it sits for 30 minuets plus.


If you can fill the VST up using the primer bulb to solve your problem,
then you need to find out where that fuel is going
and why it is not filling back up once you restart after a hot motor sittting for 30 + min

how did the tech make sure the cooler has good flow?

[captron904]

Problem is more frequent when its hot outside. Once the engine cools down over night it starts and runs perfect until later in the day. Always runs great, but looses prime (air in fuel line) after engine is off 30 plus minutes, and is hard to start.