anti-siphon valve location - mid cabin

[BobCT]

Long story short, my Stb engine doesn't get any gas from my Stb tank. Used the crossover to my port tank and it runs fine, that's how I got home today.

Sounds like a bad or clogged anti-siphon valve but I'm not sure where it's located? I removed the vent line and fitting from the top of the tank but that just looks like a straight fitting.

Tank has a little under 1/2 tank, same as the other. This started out as a 2,500 mis/stumbling after coming back in 5-6 footers last week. Changed all the filters but finally narrowed down the problem to the tank today.

thanks,

Bob

[prowlersfish]

should be right at the tank screws in to the top of the pick up where you conect the line

[k9th]

Agree with Paul and mine are small and "look like a fitting". They are , in reality, inline check valves and are small.

[Big D]

It's not on the vent side. It's on top of the tank where the fuel line that supplies the engine is connected to.

[koviak]

Bob, I have the same mid cabin (1989) with the same symptoms. Trace your fuel line to the forward top section, there will be a aluminum piece into a brass 90 elbow. That aluminum pc. is the anti-siphon valve,( $14.00 at WM). Make sure to use gas/alcohal rated paste sealant on threads.
I have been trying to solve this same issue on my port tank. Anti-siphon valve replaced with no change. Also removed the pick up tubes from the tanks to check for clogged screen. These are 5/8" dia. copper tubes with ends cut at 45 deg. angle, will not clog unless very large debris is present. I am going to connect my electric fuel pump thru filter and transfer fuel out of tank to see if I clog or lose suction.

[BobCT]

If that's a stock item, maybe I'll pick one up today just in case that's it. I haven't tried running it with the fill cap removed, I guess that willl rule in/out a bad valve.

So there's more than one pick up tube? Where are they located?

I was in really rough weather and I'm sure I stirred up a lot but 5/8" is huge.

thanks,
Bob

[BobCT]

which I can't find anywhere. I found one 1/4" x1/4"....the only 3/8" npt is to a hose barb, I need threaded on each side.

Any ideas?

This is something we'll all need to know especially if finding parts is a problem.

Bob

[prowlersfish]

Can you clean the old one ?

[BobCT]

but I'll give that a try.

[Dan Faith]

I had a very similar problem, thought it may be water in the fuel. When I got into it I found the reduction fitting going into the tank was cracked and was just sucking air. Replaced it with a 90 cent fitting and no more problems. Look at all the fittings for cracks they can be hard to see.

[BobCT]

A new one fixed my problem and based upon what I saw, I would consider these "wear" items.

My boat has never hit 4k+ RPM's since I've owned it. The WOT RPM's have actually been dropping slightly over the course of the season and would settle in around 3,700. During my survey late last year, the results were 3,900 and 3,800.

After changing both valves (one failed and the other proactively), I hit 4,100 twice this weekend. Max speed went from 20 knots to almost 24. That's a little over 27 MPH which seems to be about right for the mid cabin. The bottom needs to be stripped and painted, I'm sure that'll add a little more.

So, the only thing that changed which resulted in amost a 400 RPM increase were the anti-siphon valves. I even did one at a time and tested the results.

If you're experiencing this kind of a problem, I would do this FIRST. It's cheap, easy and should be done anyway. Eventually they will fail completely and you won't be able to pull any gas from the tank.


Bob

[tsawyer]

So what was the part # and where did you get it?

This would be good info to complete this thread for future searchers.

And if they're cheap and easy to replace, I might just add them to the to-do list.