Anti-siphon Valves
 

Just an f.y.i., my engines wouldnt rev much past 4000r.p.m. without cutting out and surging, they ran fine up to that point.
I replaced the fuel water separator filters and still didnt help.
It turned out to be a bunch of debri stuck in the anti-siphon valves at the fuel tank. Cleaned out and everything is all good.
Nice easy problem for once. Thought I would pass it along.

Good advice.
I lost a 600hp 502 partly because of my anti syphon valve a few years back. An 89 cent replacement would have saved my engine if I would have known to check/remove that stupid valve. If your boat is more than a few years old, or you're adding horsepower the anti-syphon valve should be checked for flow.

Where is the ant-syphon valve located

At the top of your tank. They look like a regular barb fitting, but have a spring and check ball in them. I had a similar instance where the boat would take off and then stall right after it got on plane. Took the fitting out and punched the ball completely out...never had a problem again.

On my current boat, just replaced ALL fuel lines from the tank to the carbs and eliminated the check valves.

Dave

So what exactly does this thing do? Why would the fuel
be moving around when the engine is off? Is this a hold
over from the carb era? Do you need one with an EFI/MPI
engine?

Its probley to prevent the fuel from draining back down into the fuel tank when the engine is shut down.

It is to prevent fuel from siphoning out of the fuel tank and filling the bilge with fuel if a fuel line were to rupture or come loose at a point that the fuel line is lower than the fuel tank itself, thus the term Anti-Siphoning. Most fuel systems are designed in a way that they are required by the Coast Guard and most likely your insurance company would deny any fuel fire claim if you do not have them. That being said, many people have removed them.

Its all in the Details!
 

Crap in the fuel tank can and should be preventable. If you have a problem with fuel quality on the water especially, carry a good fuel filter funnel and stain the fuel as you add it!
I also wanted to say that some builders and boat owners don't always size the anti-siphon valves required by law properly.
A 3/8" anti-siphon valve as about a 1/4" maximum size orfice at the spring loaded ball and therein lies a big problem also, even on new boats. This is really a 1/4" size line restriction!! If you are running a bigger horsepower engine or upgrading the power on your exisiting engine then make sure you upsize the anti-siphon valve size and all the line sizes and fittings to the filter, pump and such to provide adequate fuel flow under loads, otherwise it could drop fuel flow rates and lean the engine and possibly do a lot of engine damage before you know it.
It just makes sense, think about it, you make more engine, you need more fuel!!

Best Regards,
Ray @ Raylar

raylar ,do your 525 103 kits,need biggers fuel lines and bigger anti siphon valve,,,,or is the increased in fuel pressure going to be fine,,,i do have your kit and didnt read any thing in the instructions about larger fuel lines

How to check?
 

Twin-Spins:

Depends on how the boat was rigged. Some were rigged with 3/8" line size and some with 1/2" line size. Also depends on how long the lines are between the tanks and the engine pumps and how the crossover systems are run.
If you think you may be running on the edge of good fuel flow, run a fuel pressure guage on the engines during a WOT run and see how much the fuel pressure drops at WOT at lets say 5000 rpms. If the fuel pressure starts dropping below about 45 psi you might want to upgrade your primary line sizes to the engine pumps and check the anti-siphon fitting size.

Best Regards,
Ray @ Raylar