Fuel tank / line issues part 2

[cpoint]

I think I mentioned this latest problem piggy back on another post, so I'll start fresh. Since pandemic, we been using the boat as weekend getaway on the water. Just to summarize where I am now and see if you guys can help me out as usual

Last season after bottom paint to start season that was the extend of our trip on the water from boatyard to our dock 50 feet away. We ran into engine problems. My trusty mechanic came by towards the end of season, did all checking and testing and we went out on the water and he found issue to be fuel line or fuel tank. And I always had port side issues from day one. Anyway assumption was fuel injectors, turned out they were fine, which is very good. Still cost a fortune but what can I do. So issue is this. as you are on your way all is fine to about 2k RPM. above 2-2.5K RPM tach start going crazy and engine starts losing power and if you continue cuts out. starts back fine and goes, but soon as you go over 2-2.5K RPM same problem. so he hooked up his own tank, no issues with tach or speed, we were up to about 24 knots. So he was bussy for rest of end of season, told me what I should do. He said blow air through the 2 hoses (1 coming from tank to switch, and one from switch to fuel filter on the engine. Since assumption is some thing is blocking the fuel flow at high speed, he said check all lines and the switch. If they are fine, he said it could be the fuel pickup in the tank. This makes sense as my tank was cleaned twice, but still there is stuff there. long story. So it's possible there may be something there blocking partially. He said I can also use compress air through the pickup line. And getting back to weekend, I went to try try these, but everything related is in a hard to get to place. So I basically started with simple step of removing the hose from engine side, and gently blew air into it by mouth, and heard the bubbling in the tank, I said that's great. so try to use compressor to get better flow, which worked for a second, then it stopped like tank or hose was blocked. so I waited 5-10 minutes and blew by mouth and heard bubbling in tank, try the compressor, air basically would not go because something was blocking it. So I gave up, am planning on trying the following next and let me know what you guys think?

1) I am going to remove the hose from engine side and tank side and try blowing air to make sure hoses are clear.
2) if they are clear, I am going to try to blow air into intake line it self. or should I remove the intake line and visually inspect and clean. I know some one here had mentioned in his case they had uses different metal for the in take line so he had rust.
And to do that I know I have to cut top off flooring to remove the intake line straight up.

Is this a good plan?

And why would air not go in constantly when I blow air in. Is the tank pressurized, is the pressure relief valve out side blocked? how to I clear that if so? Or I am thinking there is something that is in the intake valve that's not letting air back because it's blocked? Only way to see that is to obviously remove intake line. Any one done that, or anyone knows the part that I would need for 2000 carver 356 intake valve? I figure if I remove, mine as well put new one in?

Thanks to all

[Viper]

Has anybody checked the anti-siphon valves? These are on top of the tank where your fuel line hooks up to. If they've never been replaced or cleaned, I would start there. It's a simple cause and pretty common, would have expected your tech to check them already though. That's where I would start.

[cpoint]

Source of the post Has anybody checked the anti-siphon valves? These are on top of the tank where your fuel line hooks up to. If they've never been replaced or cleaned, I would start there. It's a simple cause and pretty common, would have expected your tech to check them already though. That's where I would start.

Viper, Thanks for reply. He did not have time, he was busy on bigger projects and was kind enough to stop by for me to take care of couple things. He would have taken care of it had there was time. He did mention that as well. At the end of the day I may end up calling him. Was trying to see if I can take care of this as it sounds like a simple issue. So should I just replace that anti-siphon valve? sounds like you are saying they don't last forever, I am pretty sure what I have their is original. I'll look for part see if I can find it on Amazon

[km1125]

For as cheap as they are, I'd just replace the anti-siphon valves. They can get debris in them and restrict flow. Also, I don't think you'd be able to blow "backwards" past them so you'd need to remove them if you were trying to see if there were any restrictions in the intake tube.

Once you remove the anti-siphon valves, you can look inside to see if there's any debris. Some can be disassembled and cleaned pretty easy, others not no easy.

[cpoint]

I did manage to blow through, so that sounds like there is an issue with them than. I am looking for the part now. At worst I guess I can remove it and go to west marine. I do not think there is a part number for carver products online.

[g36]

Post by mistake can't remove

[bud37]

I agree ...put some new anti siphon valves in service, that will cross something off the list even if they are not the problem......fairly cheap items.

[g36]

You have more than 1 tank to pull fuel from, are you having issues pulling from either tank? The only common fuel line is from the fuel selector valves to the engine. Anothr option You could temporarily swap fuel lines from the genset pickup as long as your tanks at least 1/2 fuel since its shorter and try that Where did the mechanic hook up the external tank?

[bud37]

Source of the post And why would air not go in constantly when I blow air in. Is the tank pressurized, is the pressure relief valve out side blocked? how to I clear that if so? Or I am thinking there is something that is in the intake valve that's not letting air back because it's blocked? Only way to see that is to obviously remove intake line. Any one done that, or anyone knows the part that I would need for 2000 carver 356 intake valve? I figure if I remove, mine as well put new one in?

The tanks are not pressurized as they are vented to atmosphere, assuming your tank vents are clear and not restricted.

Actually on the surface it seems like those anti-siphon valves are working but they should still be checked for debris and operation......basically just a one way valve depending on the maker....allows fuel out of the tank when there is suction on the engine side ( engine fuel pump running ), but if the line breaks or there is a leak with no suction the valve does not allow the fuel create a siphoning action and drain out to the bilge.

[cpoint]

Source of the post You have more than 1 tank to pull fuel from, are you having issues pulling from either tank? The only common fuel line is from the fuel selector valves to the engine. Anothr option You could temporarily swap fuel lines from the genset pickup as long as your tanks at least 1/2 fuel since its shorter and try that Where did the mechanic hook up the external tank?

I think genset line has same issue, which I am going to check once I start working on the port side one. That has not pulled fuel from port tank in 2-3 years, never had a need for. But pretty sure the anti-siphon valve on that is bad.