anti-siphon valve

I fixed my hestitation and ultimate stalling issue by replacing one of my anti-siphon valves the other day. $14 part, easy fix. This is something that could leave you in a tough spot (i.e., losing an engine when docking or rough weather). This was on my winter "list" last year but just never got around to it.

Ironically, I replied to another post just a couple of weeks ago asking what the work around would be if this failed on the water and then it did

I would strongly recommend changing them on both tanks at your leisure. That's what I did and have another new spare on board. For me, I also hit the bonus round. I've been half heartedly chasing my lack of WOT RPM's throughout the season. I was getting maybe 3,600. After changing the valve on my Stb side, I could immediately feel the difference in the slip. Sure enough, I climbed over 4,000 during my test run... the first time it's done that since I bought the boat.

I think these might actually be a wear item. Probably not from use but from dirt accumulating over the years. If you're experiencing any of the above symptoms, put in a new valve(s). It's a good thing to do anyway...


Bob

P.S. - the "valve" really doesn't look like much. It just a brass fitting sandwiched between the fittings on the tank/line. If you need 3/8" NPT x 3/8" the only place I found them was through Silverton parts. (I have a Trojan).

I'm incline to agree with you about the need for periodic replacement....now the question is at what frequency?

good question, mine were original at 22 years so less than that

I know some people have had success cleaning them but you have to figure the tolerance on the spring will change over time. What does that do?

If had a WOT issue in the future, I would change the anti-siphon valves first. Easy thing to rule out and cheap enough. I got the impression from all the posts I read that they're typically a work/doesn't work item but that wasn't the case for me. It was a gradual failure over at least a year.

Bob

Bob; was it possible to look inside and see what the trouble was? I had some aluminum swarf in one of mine a few years after a tank replacement. Good find on the source for a high quality brass one!

Dave - no it actually looked fine. I didn't try and clean it though so I might have seen some crud if I blew it out.

I lucked out getting it through Silverton directly.

What kind of space did you have to remove the valve? I am assuming this is the valve that is screwed into the top of the tank with the pick up tube attached on one end and the fuel line on the other? Does the pick up tube come out with the valve?

Scott,

I was able to unscrew the fuel line and then remove the valve. The 45 which threads into the top of the pick up tube stayed in place.

The couple I disected were 'corroded' and the majority of them were aluminum.

I had problems with mine clogging with sawdust & aluminum chips on both tanks when the boat was new. Luckily, it never happened to both at the same time. They are brass & look from the outside just like a normal hose barb. Sneaky little things. I had to clean them a few times until I placed a screen in the bottom of the pick up tubes. Haven't had a problem since. The new fuel injected engines recommend solenoid valves at the tank. Supposed to have less restriction then the spring loaded valve. However, they are pricey so I left the old valves in. I checked fuel pressure @WOT with & without the old valves & it was the same. I also tried to start a siphon (don't ask how) & could not.

Checking the pressure just lets you know the pump can handle the feed system in front of it. You want to minimize the pressure drop at the pump's inlet....need a vac gauge to check that.

Could a partially clogged valve affect the fuel pressure when measured at the rail through the Schrader valve? My stb, (fuel injected) fuel pressure is @ 4-5 psi less than the port engine and below spec of 43 psi at idle. Have put new pump in, new regulator, clean filters...both primary (screen) and 10 micron Racor element. Both engines pull fuel from single tank with separate lines.

If it offers a large enough restriction, it could not only limit the pressure the pump develops but also limit the delivered volume. The last spec I checked for a MPI EFI setup (SBC) was 2" Hg max vacuum at the pump's inlet fitting (also has the 43 PSI min pressure spec).