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

[Lou C]

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....

 

[Scott Danforth]

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

Make sure you know the number when testing

 

[JustJason]

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....

HOW TO: Testing your boats fuel system.

Note, this was originally posted courtesy of Don S. Minor edits and pictures added by CaptJason A lot of you folks out there seem to be tearing into carbs quite a bit. Before you choose to open up a carb, you really need to look at what's feeding the carb first, and that is the boats fuel...

forums.iboats.com

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.

 

[kd4pbs]

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.

 

[dingbat]

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

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)

Permatex® Form-A-Gasket® No.2 Sealant, 3 OZ - Permatex®

www.permatex.com

 

[jimmbo]

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

 

[JustJason]

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

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.

 

[Lou C]

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.

 

[Pmt133]

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.

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.