Anti siphon valve

[Drafter]

Hey guys,
I've got an 85 10 meter sedan that I'm pulling my hair out with. My starboard motor is shutting down after about 30 minutes of cruising. It will restart with a good amount of throttle, but only for a minute or two and then stall back out. After sitting for a while, it will run a little longer. Initially starts, idles, and runs great. I now suspect the anti siphon valve after a good beer drinking floating session with a couple of other old boat owners over the weekend. Carb was rebuilt last week (by a qualified mechanic), fuel pump week before that, new coil over the weekend... I would like to replace this next weekend. I believe I still have copper lines where this valve is up to the canister. Can anyone tell me what size valve this is so I can get one ordered? 1/4", 3/8", flare on one side...?? NPT on both sides? (or) are there other thoughts or possibilities on this?
Definitely appreciate any advice.

[Scorpion07]

I have no advice, but have the exact same issue and did all that you have.......and then some.
I even pulled the valve once and it was plugged. It's a real simple device and I don't see how they could go bad on their own.
Aside from the size of the valve, please repost on your results.

[g36]

on my 78 f32 with copper lines it was this, does yours look like this? the valve is in the circle its 3/8" NPT x 3/8" screws to the 90 degree fitting on the tank and the other side has the flare to gas line adaptor. in addtion you might disassemble and visually inspect to note any issues i.e. stuck/sticking or foreign object

[gettaway]

I had the same issue with our Silverton 37 C (Crusader 454') when we bought it, and found the issue to be the anti-siphon valve,It was packed with debris, i cleaned it out and it fixed the problem. You can see in the photos that the valve looks like am NPT to Flare adapter, but its actually a spring loaded ball check valve. when you pull it out, make sure you an easily blow through the valve in the flow direction with very little resistance and it doesnt hang up, its supposed to only prevent a siphon in case your carb float sticks open or a fuel line or filter were to break



You can see the crap that plugged up the anti siphon

[Drafter]

Awesome, thanks guys! I ordered one this morning based on your pics and hope to get it figured out this weekend. Appreciate the help a ton.

[K4282]

hmm, im recently having a similair problem on my port motor, on my old 26 Silverton it was plugged up risors, my Trojan sat for awhile before me, the carb was bad I bought a brand new one, the lines had allot of gunk in them, this seems like a much cheaper fix, where do I buy one of these parts and wheres it located

[woodendave]

Check fuiltank vent. If removing fuilcap reliaves proplem thats it.

[Drafter]

I pulled the anti siphon valve out, cleaned it up with a few shots of carb cleaner, and was able to blow through it in the outflow direction. I assume it's in good shape. Haven't had a chance to lake test it yet. I would do back flips if that actually solved my problem. I thought about the vent line. I have a single tank on my 10 meter and the port engine has no such issue. In addition, the vent has no problem with letting me know that my tank is full when I fill up which is often, as it's also time to cut a hole in the deck and replace the fuel sender. At least if it's full I know how much gas I have. Now it makes me think something is getting hot in the ignition and shutting off. Cooling off a bit, and then allowing a restart. My ignition is an electronic MSD 6AL unit with MSD coil. I replaced the coil last weekend as part of my attempt to sling parts at it until something worked. MSD units will shut down when battery voltage drops, but then why would it restart? Batteries don't magically re-energize with no input from either the alternator or a charger.
I'm really ready to get this figured out.
For those curious, the anti siphon valve is in line right at the exit of the fuel tank at the 90 degree fitting and before the fuel line starts. Mine was 3/8npt threads on both ends with an adapter on the down flow side screwed in to connect a flare fitting on the copper fuel line. The other side screwed into the 90 degree fitting screwed into the tank bung.

[g36]

For those curious, the anti siphon valve is in line right at the exit of the fuel tank at the 90 degree fitting and before the fuel line starts. Mine was 3/8npt threads on both ends with an adapter on the down flow side screwed in to connect a flare fitting on the copper fuel line. The other side screwed into the 90 degree fitting screwed into the tank bung

see above pic #1

[mikeandanne]

Here are a couple ideas----- next time it shuts down ,take off the flame arrester and look in the carb throat and have someone pump the throttle to see if the carb is dry ( there should be fuel coming from accelerator pump squirters,it may take a couple shots to empty but it should not refill if the bowl is dry)----- if it is then check for air leaks to fuel line to that engine,bad valves etc. ----- if carb full then ignition,if the 6 al is one of the newer digital ones ,that may be your problem,the older analog ones are bulletproof----- I went through a few and sent them all back and put the old analog back and never had any more trouble----- Mike

[Drafter]

Thanks Mike. Yes, it is one of the older versions. I've seen the newer digital versions and even thought about buying one to see if it solved my problem. That's good to know.

[hanybop]

heres something to look at, maybe the fuel tank vents are plugged, as you state the engine will run for half a hour then starve for fuel, it could be creating a vacuum in the tank after a period of time and eventually creating more suction than the fuel pump fuel pump can draw, insects like to make there homes inside these tubes especially if the screen is missing,

hope this helps

cheers paul

[rbcool]

I had a similar problem couple yrs ago..... suddenly the Stbd engine wouldn't start. Replaced fuel filters with no improvement. Remembered seeing a post here about the anti-syphon valve. Removed it and reinstalled the fuel line with out it (it's in-line). Engine fired right up. Ran her like that until I recieved 2 new ones from this site.
RB

[Drafter]

Thanks everybody for your replies! Turns out, it appears it was the ignition box. Finally just cut everything out, and bought a new digital 6AL MSD box because the analogs were no longer available (at least locally). Could have been bad connections but I was tired of trying things. The new box is wired directly to the corresponding battery vs the starter power and everything seems to be working. Been out 4 times, once for 3 hours, and no issues. Finally nice (knock on fiberglass) to enjoy my new boat and come back to the dock with all of the motors that I left with!
With that, this weekend will involve a jig saw, a big hole in my nice cockpit, and a new fuel sender!

[g36]

WHOA hold up there mr. jigsaw
are you sure you have to cut the deck? if you had room to remove the antisiphon valve i think you would have room to install a new fuel sensor.i would try unscrewing it first and see if you cant wiggle it out. its probably a swing arm unit and you'll be suprised at how small an area you need to get it out. might need to get an offset screw driver etc.and it might be tight but cutting a hole is a shame for this.