If you're wondering if your anti siphon valve is stuck, or clogged, here's a test....

I had mine replaced years ago, always wondered if there was a way to test it to make sure it's not starting to stick again. I have a pressure and vacuum tester for the outdrive, so I rigged up a way to put a vacuum on a new un-installed anti siphon valve and see at what point it opens, about -2" of mercury. So if it holds much more vacuum than that, a good sign it might be contributing to a fuel delivery problem you could be having. This could be useful if the old one has been installed a long time and might not come out easily....

All the AS valves have a number on them. That is the vacuum that they open.

Make sure you know the number when testing

Lou C said:

I had mine replaced years ago, always wondered if there was a way to test it to make sure it's not starting to stick again. I have a pressure and vacuum tester for the outdrive, so I rigged up a way to put a vacuum on a new un-installed anti siphon valve and see at what point it opens, about -2" of mercury. So if it holds much more vacuum than that, a good sign it might be contributing to a fuel delivery problem you could be having. This could be useful if the old one has been installed a long time and might not come out easily....

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I wrote that back in 2008. That will tell you how to test it. The only caveat is that it was really written for older inboard carbureted engines. On all modern-day EFI/DFI/HPDI/GDI engines, you really don't want to see more than about 2.5 inches of mercury restriction-wise. If there is more than that, it could be a number of things, but usually the anti-siphon valve.

There is another way to test the valve itself using a section of clear nylon tubing zip tied to a 3 foot yardstick. I'll take a look and see if I still have that old testing procedure, but I doubt it.

And sometimes, you just gotta go with your gut. Had a Chap Signature that unfortunately had a Yamaha I/O. Not that this is related to this particular issue, but I thought I'd mention that to possibly garner some sympathy....
I could cruise along just fine for several minutes, then it would bog and stall. Wash, rinse, repeat. I tested the anti-siphon valve and it was fine. Problem persisted. Finally, I teed in a vacuum/pressure gauge to the fuel line. It became readily apparent that the fuel feed was getting clogged. Removed the spring and ball in the valve and all was well again. After a year, I reinstalled the spring and ball and never had another issue. Eventually I realized some numbscull used silicone to seal the sending/pickup assembly to the tank. Cut the fuel filter open and saw the bits of silicone.
Let this be a lesson: Only use fuel-compatible sealant if you're going to use sealant. The only kind I use on fuel systems is Permatex #2.

kd4pbs said:

Only use fuel-compatible sealant if you're going to use sealant. The only kind I use on fuel systems is Permatex #2.

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Interesting note on Permatex #2

While they claim chemical / solvent resistance to gasoline, they don't recommend for use where there is prolonged exposure to aromatic solvents and additives.

Funny since 25% of every gallon of gasoline in the United States is comprised of the aromatic hydrocarbons (solvents)

The one on my Boat was stuck closed when I took it out the First Time. Engine had been run from a Separate Tank at the Dealer during Prep. That Valve no longer exists in my boat

jimmbo said:

The one on my Boat was stuck closed when I took it out the First Time. Engine had been run from a Separate Tank at the Dealer during Prep. That Valve no longer exists in my boat

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I would be careful.

If your fuel system is designed in a specific way, some form of antisiphon protection is federally required, be it a valve or a solenoid.

I recently completed an investigation on an insurance claim where the boat, outboard powered, started and ran fine on a Monday. On Tuesday, the boat exploded, sending 2 to the burn center. Here is what we found.

1. Antisiphon valve removed.
2. Fuel/water separating fuel filter rotted out, and drained into the bilge. As it was draining, because there was no antishipon protection, about 1/2 the fuel in the tank also went into the bilge, and not just the little quart or so that the filter holds.
3. There was a loose battery cable connection.
4. Somebody installed a non-ignition-protected self-resetting circuit breaker for a bilge pump, which shared a common space with any/all fumes in the bilge.
5. Somebody installed a bilge pump and did not use heat-shrink connectors, but rather, basic crimp connectors, which were poorly done.
6. Owner purchased the boat new, has owned it for 3 years.
7. The above-mentioned somebodies were paid technicians.
8. Still trying to work out who pulled the valve, as Dometic was there for the inspections, and they insist all of their fuel tanks get shipped to the boat builders with the valves installed. So far, nobody has owned up to that.
9. The insurance carrier has not decided if coverage will apply. In their eyes, because the vessel was not in compliance with federal law, it was not seaworthy, and maintaining a seaworthy vessel is an implied part of the policy.

Luckily, this was 1 boat and 2 people. It could have been a lot worse.

Wow thanks for posting this it is a good warning for any of us DIY guys to not take short cuts, not bypass safety measures put in place for good reasons, etc.
What doesn't really make sense or is at least surprising is that the fuel filter rotted out on such a new boat. I always change them every year anyway but I can't imagine it rotting out that fast unless there was salt water in the bilge like 100% of the time...
It also goes to show you that outboard owners can't be cavaliere about fuel system safety just because they don't have an inboard gas-powered boat.
I recall another case that was on the old Seaswirl Striper board where a flash fire happened because the gasket for the cover for the fuel gauge assembly had been leaking unbeknownst to the owner and somehow the vapors were ignited, and he wound up going to a burn center as well.
Some years back I added a gas vapor detector to my boat but still always check with the sniff test.

JustJason said:

I would be careful.

If your fuel system is designed in a specific way, some form of antisiphon protection is federally required, be it a valve or a solenoid.

I recently completed an investigation on an insurance claim where the boat, outboard powered, started and ran fine on a Monday. On Tuesday, the boat exploded, sending 2 to the burn center. Here is what we found.

1. Antisiphon valve removed.
2. Fuel/water separating fuel filter rotted out, and drained into the bilge. As it was draining, because there was no antishipon protection, about 1/2 the fuel in the tank also went into the bilge, and not just the little quart or so that the filter holds.
3. There was a loose battery cable connection.
4. Somebody installed a non-ignition-protected self-resetting circuit breaker for a bilge pump, which shared a common space with any/all fumes in the bilge.
5. Somebody installed a bilge pump and did not use heat-shrink connectors, but rather, basic crimp connectors, which were poorly done.
6. Owner purchased the boat new, has owned it for 3 years.
7. The above-mentioned somebodies were paid technicians.
8. Still trying to work out who pulled the valve, as Dometic was there for the inspections, and they insist all of their fuel tanks get shipped to the boat builders with the valves installed. So far, nobody has owned up to that.
9. The insurance carrier has not decided if coverage will apply. In their eyes, because the vessel was not in compliance with federal law, it was not seaworthy, and maintaining a seaworthy vessel is an implied part of the policy.

Luckily, this was 1 boat and 2 people. It could have been a lot worse.

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So I have to ask. The way the CFR reads to me seems that if the entire fuel system is above the static max height of the tank, no siphon protection is needed. Or am I interpreting that improperly? I have a siphon valve installed, but I had it off for a while diagnosing a different issue.

I am not a very experienced boat mechanic but I have seen some truly bad maintenance come out of some of the local dealerships. Sometimes the level of stupidity coming out of a “professional shop” is mind boggling. One boat had a battery disconnect switch installed next to the battery with a hot wire hooked to the switch and no wires coming from the switch. That’s right, everything was connected to the battery as if the switch wasn’t there. Electric steering pumps that constantly draw power hard wired to the battery instead of the disconnect. SeaStar steering cylinder hardware left loose. The boat lost steering with less than 10 hours on it while crossing the lake when the nut on the end of the steering tube fell into the bilge. I had some VST maintenance done on a Suzuki. The next time I changed oil on the boat I found the high pressure fuel filter hanging by a couple of threads of one bolt. The other bolt was missing. I found it and a hat bushing in the middle covers. The hat bushing came from a VST isolation mount where they installed a single flat washer to replace the bushing they dropped. Just a few items from a very long list of things I found on brand new boats or following dealer maintenance on used.

Every mechanic misses stuff and screws up now and then. If they don’t then they aren’t working but it’s getting to the point I don’t think they even try to do a good job anymore.

Lou C said:

Wow thanks for posting this it is a good warning for any of us DIY guys to not take short cuts, not bypass safety measures put in place for good reasons, etc.
What doesn't really make sense or is at least surprising is that the fuel filter rotted out on such a new boat. I always change them every year anyway but I can't imagine it rotting out that fast unless there was salt water in the bilge like 100% of the time...
It also goes to show you that outboard owners can't be cavaliere about fuel system safety just because they don't have an inboard gas-powered boat.
I recall another case that was on the old Seaswirl Striper board where a flash fire happened because the gasket for the cover for the fuel gauge assembly had been leaking unbeknownst to the owner and somehow the vapors were ignited, and he wound up going to a burn center as well.
Some years back I added a gas vapor detector to my boat but still always check with the sniff test.

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It rotted out from the inside out. The boat builder (who shall be nameless) put the filter in the worst possible spot. I don't think the technicians knew it was even there. I didn't see it until I took an angle grinder to the boat and personally cut the splashwell out of the boat. What's interesting is that there were invoices stating it had been changed, but my gut tells me it never was. The reason I say that is that the invoices all list a brand and part number for the filter, which wasn't the filter we took out of the boat.

Pmt133 said:

So I have to ask. The way the CFR reads to me seems that if the entire fuel system is above the static max height of the tank, no siphon protection is needed. Or am I interpreting that improperly? I have a siphon valve installed, but I had it off for a while diagnosing a different issue.

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The ABYC standard, which is the esentially same as the CFR, just reworded, and more strict says:

24.15.10 Fuel distribution systems shall be provided with anti-siphon protection by keeping all parts of fuel distribution and return lines above the level of the tank top from the tank to the carburetor inlet or its equivalent, (e.g., throttle body, port fuel injection, or a location where fuel leakage cannot enter the boat when the boat is in its static floating position); or

24.15.10.1 by installing an anti-siphon device at the tank withdrawal fitting, or along the fuel distribution line, with a rated siphon protection head and flow rate greater than required for the installation and a screen complying with
H-24.19.2.10.2 installed on the tank side of the anti-siphon device; or

24.15.10.2 by installing an electrically operated valve at the tank withdrawal fitting, or along the fuel distribution line, connected to be energized open only when the engine ignition switch is on and the engine is running;

24.15.10.3 or, if the fuel tank top is located below the level of the carburetor inlet or its equivalent, and the fuel line is rigid metal or USCG Type A1-15 hose, by installing a manual shut-off valve directly at the fuel tank connection, arranged to be readily accessible for operation from outside the compartment.

24.15.10.3.1 If the length of fuel line from the tank outlet to the engine inlet is greater than 12 feet (3.6 m), a second manual shut-off valve shall be installed at the fuel inlet connection to the engine.

24.15.11 In outboard engine powered boats with permanently installed fuel tanks, the fuel distribution system shall be installed by the boat manufacturer.

24.15.11.1 Fuel distribution lines provided with anti-siphon protection shall be installed in outboard engine powered boats equipped with permanent tanks,
and

24.15.11.1.1 fuel line connections to the engine shall terminate at the stern where fuel spillage will not enter the boat.

Jeff J said:

I am not a very experienced boat mechanic but I have seen some truly bad maintenance come out of some of the local dealerships. Sometimes the level of stupidity coming out of a “professional shop” is mind boggling. One boat had a battery disconnect switch installed next to the battery with a hot wire hooked to the switch and no wires coming from the switch. That’s right, everything was connected to the battery as if the switch wasn’t there. Electric steering pumps that constantly draw power hard wired to the battery instead of the disconnect. SeaStar steering cylinder hardware left loose. The boat lost steering with less than 10 hours on it while crossing the lake when the nut on the end of the steering tube fell into the bilge. I had some VST maintenance done on a Suzuki. The next time I changed oil on the boat I found the high pressure fuel filter hanging by a couple of threads of one bolt. The other bolt was missing. I found it and a hat bushing in the middle covers. The hat bushing came from a VST isolation mount where they installed a single flat washer to replace the bushing they dropped. Just a few items from a very long list of things I found on brand new boats or following dealer maintenance on used.

Every mechanic misses stuff and screws up now and then. If they don’t then they aren’t working but it’s getting to the point I don’t think they even try to do a good job anymore.

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See my blurb in May's issue of Trades Only Today - https://tradeonlytoday.com/columns-blogs/knowledge-is-power/

I was quoted as writing, "Jason says he often finds that in the marine service trade, skill and effort are inconsistent, but he believes the industry can do better."

What I actually wrote was a lot harsher.... The editor paraphrased what I actually wrote to make it a little more PC.

Here is one that just came to light for me. A boat put on consignment last year just came back because it hadn’t sold and some other boats are having issues (ripped out ski tows and the like). The shop that was supposed to clean it up and put it on consignment charged $1,000 to winterize it (Volvo Penta I/O). I do not know their process. No idea if they put antifreeze in it or not. What I do know is they left a clamp off a cooling hose which blew off while crossing the lake and rapidly filled the bilge with water and the oil had not been changed. I found a water drain plug in the bilge when I cleaned it out. I also replaced the impeller. It was missing a fin. The manager was told the boat had been fully serviced.

The boat looked good from the outside but the bilge was an oily mess. I was looking for the cause when the decision was made to sell the boat. I took another stab at it while I was doing the oil change a couple of days ago. The steering cylinder currently is leaking a drop or so a second. I don’t hold the leak against the shop. The last stretch of inactivity made the leak easy to find but I do think hosing out the bilge should have been included in the cleaning.

Some maintenance facilities aren’t the only poor performers. The picture was taken after 2 different detail shops had “cleaned” a boat. Neither detail shop bothered to lift a seat cushion. I spent all afternoon vacuuming and flushing rat turds out of it. 20 ft ski boat.

Jeff J said:

The shop [...] charged $1,000 to winterize it (Volvo Penta I/O).
[...]
vacuuming and flushing rat turds out of it. 20 ft ski boat.

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Sounds like the rats were busy on this one. And they were nice enough to leave you with their turds from the year prior when they charged that much to do a simple winterization.

kd4pbs said:

Sounds like the rats were busy on this one. And they were nice enough to leave you with their turds from the year prior when they charged that much to do a simple winterization.

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Different shops. Turds long gone before the $1k winterization. I would be doing winterizations if I thought I could get $1K per boat.