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Yamaha F225 starving for fuel

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  • Yamaha F225 starving for fuel

    I think I've got a fuel issue but I'm getting stumped at this point. I can't run any more than 3/4 throttle. Push past and it bogs down and looses RPM. 4K RPM is all I can get until it starts to come up on plane then it will slowly gain speed and RPM up to about 5200 then that's it. I've replaced the spin on filter, the small cartridge filter inside the hood, the u shaped filter on top of the VST tank, and the VST filter on the bottom of the high pressure pump. I've checked both of the little aluminum check valves and they work like they should. Now I've found an aluminum part on top of the VST tank that connects to the intake that seems to be stopped up. I can't blow air through it in either direction. Liquids won't go through it (PB blaster, brake cleaner, acetone) even when forced by the compressor. In the diagram attached it's piece # 25. Can I drill a tiny hole in it like with a #80 drill? What does the stupid thing even do? I don't want to buy a new one if I have to because it's $220. Any help would be appreciated.
    Attached Files
    '90 Tuppens 231 Polk City, FL


  • #2
    Fuel lines and primer bulb?

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    • #3
      Primer bulb has been deleted, and the fuel lines are all good, as far as I can tell.
      '90 Tuppens 231 Polk City, FL

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      • #4
        I did a quick search on that part and found. https://www.yamahaoutboardparts.com/...r-orifice-vent

        https://www.yamahaoutboardparts.com/...b-bogging-down
        Last edited by Cyrus; 07-01-2020, 09:28 PM.

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        • #5
          I found that article and several others on that site that were helpful. I was able to figure out what I think is correct in the part's function within the system. I was also able to get it cleared out, so that air will pas in either direction. After re-installing it and doin a lake test it seemed almost fixed on the first run from the trailer when it was cold but still had a slight hesitation that you can hear in this video: https://www.youtube.com/watch?v=IZF8QvF_mvg . After running it for 15 minutes or so this is what I was getting: https://www.youtube.com/watch?v=aeCz6thvkl4 . This video is of the GPS unit where you can see the RPM of the motor better: https://www.youtube.com/watch?v=HXV6m6MeAzA .

          I have replaced the every filter on the system and checked all the lines and components under the hood, and it all seems to check out. It ran much better yesterday than it did on Monday, after I repaired the orifice, but it's still not right. It was only me in the boat for the test so I know when I load the boat I'll be back in the same creek. I got to thinking yesterday that during the off season I added the command link cable to my engine and it was a couple months before I used the boat. I don't remember when my trouble started though, I guess it's possible that I have the line pinched in the rigging tube and it's been slowly getting worse over time. I am going to pull it apart this afternoon and see if I can find anything wrong. I have my doubts though because while running yesterday I had the hood off and the clear filter under the intake plenum never looses fuel. Right now I'm at a loss, I don't know what it could be and I don't want to keep throwing parts at a problem. Up to this point everything I've done could be justified as maintenance, but the HP pump is not a cheap "maintenance" item.
          '90 Tuppens 231 Polk City, FL

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          • #6
            I am trying hunt down a issue on my Mercury right now too, it is something how many things "can be" the problem. In that second link the guy was describing trouble shooting fuel pressure issues. If you do not have a fuel pressure gauge you can go to an auto parts store and they will loan it to you with a deposit. I did not notice till I got home that the fuel pressure gauges they loan you do not have a fitting for the Shrader valve. So, I removed the valve stem and used some hose and a hose clamp over the valve If I go borrow a gauge again I will ask about the fitting before I leave.

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            • #7
              How are the anti-siphon valves on the tank?

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              • #8
                Does anyone here know Yamaha??

                I'm still having issues with this thing.

                Ran it yesterday and for the first 10 minutes I was only able to finagle 5200 rpm out if it, but the longer it ran the worse it got. By the 30 minute mark I could only get 2800-3000 rpm. Priming the ball while running changes nothing. I don't think I'm getting any air on the suction side of the LP pump because when the LP pump is running there are no bubbles and the pressure is steady at 11psi. Rail pressure is what is causing the problem. I'm getting the 44psi with the key on. It drops to 38psi when cranked and idling. Upon acceleration when cold the pressure starts to go up but falls after reaching half throttle. It makes it to 42psi but beyond half throttle it drops to 25psi or so. The hotter the engine gets the further and faster it seems to drop. Based on this my questions are this:

                1) Does the HP pump run at a constant speed or does the engine speed the pump to meet demand?

                2) If the pump speed is con*****ed what gives the signal? TPS?

                3) Is it common for a pump like this to get weak and not supply enough fuel especially once it's hot. (I'm in central Florida so the air temp is in the mid 90's with the water temp nearly 90 as well)

                At this point I'm leaning toward the HP pump not supplying adequate fuel to the rail and once it gets hot it supplies even less. This would also explain why it seemed to be a gradual problem when it first started.

                To date I've done everything below:

                1) Replaced the spin on filter.
                2) Replaced the small filter under the intake plenum.
                3) Replaced the "F" filter.
                4) Replaced the VST screen.
                5) Checked all the check valves.
                6) Inspected and repaired any and all lines under the hood.
                7) Replaced all fuel lines from the tank to the engine.
                8) Checked tank vent lines.
                9) Checked LP pump pressure (11-12 psi).

                I don't know about the ASV on the tank. I can't pull it without cutting a bigger access in the lid and I'm really not wanting to do that.

                I'd be open for a phone conversation if it's easier. I'm to the point that it's about to go to a shop or the sand at the bottom of the lake LOL.
                '90 Tuppens 231 Polk City, FL

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                • #9
                  The high pressure pump is not 'throttled'.
                  There is a resistor inline with the high pressure pump. It is possible that it has issues as it gets hot but that would not be my first guess as to the problem.
                  First thin to try that is simple is to run the boat with the fuel cap off. It is possible that you have a venting issue and that takes time to show up depending on how blocked the vent it , how hard the motor is running and how full the tank is. The lower the gas level, the longer it takes to show up. I wouldn't suspect that is your problem.
                  You have to connect a fuel pressure gauge to see if the pressure is correct and steady. Knowing that will help determine if the problem is fuel starvation or maybe something else.
                  I would also suggest that if possible you run the boat until the problem occurs and immediately shut off the motor. Pull the cowling and look at the clear fuel bowl. It should had gas in it but also some air at the top.
                  Those are the basic tests. The results will determine where to look next.
                  You can do the fill cap off and the shut down after the problem pops up on the same trip.

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                  • #10
                    It is not a tank vent issue, I ruled that out very early on. The clear bowl never loses fuel or has any level change inside the bowl. I put a pressure gauge on the pressure side of the LP pump and the pressure is constant at 11-12 PSI. I think I've got it narrowed to the HP pump or supporting components.
                    '90 Tuppens 231 Polk City, FL

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                    • #11
                      A fuel pressure gauge on the high pressure fuel rail will tell you if there is a delivery issue. I don't have the manual for that motor handy and can't say what the rail pressure should be but if it operates like the 2 strokes, the rail pressure should remain fairly constant at all times of operation.
                      There may be ( probably is) a pressure regulator valve on the output side of the vst that could be bad.

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                      • #12
                        I broke down and took it to my mechanic. Turns out the vst filter that I bought at a local shop had some sort of film over the screen. The mechanic had never seen anything like it. He showed me the difference between the one I installed and the one he installed and it was significant. While it wasn't dirty you couldn't see through it. He didn't know what could've caused it but he suspected that it was bad from day 1, because it never ran any different after I installed it. And of course since there was no change I ruled it out as being the issue.
                        '90 Tuppens 231 Polk City, FL

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