Anti syphon valves

Wow. We have all learned something with this information today. Thanks for your work on this and for sharing with everybody.

Now I wonder what the "rating" is for the valve on my boat? I just grabbed the one off the wall at the marine supply place a couple years ago. It works, so I suppose I'm OK. :)

I was surprised to see them rated with a WC rating. A CV value would be more accurate.

Gary, the early boats had copper lines with a shut off valve near the engine and no anti syphon valve. I don't know when they started installing anti syphon valves, but I've installed them in our Classic and Mustang along with a water/fuel separating fuel filter. Without the anti syphon valve, the filter will dump fuel when changing the canister. Moeller does make a barbed fitting with a ball valve that's easy enough to install in our case, but if the anti syphon valve is not the source of our problems, I'd re install it.

SNobsessed wrote: Interesting trivia, I wonder why the difference in WC from small to larger engine. Seems counterintuitive. Pete needs to investigate this!

My thought is the 30 with the weaker spring allows the ball to travel all the way to the outlet side of the valve and cause an obstruction when used with a higher hp engine. However, I'm a little skeptical because most valves I have seen for sale are 30s and with no information on the label and no one really knowing anything about this, I've got to think that there are plenty of boats out there with the wrong valve that are operating just fine.

I completely understand that. I wonder about the long-term. The valve serves a function of some sort. The name of it makes me think that there may be instances where the fuel would naturally want to flow backwards and thus starve the engine. I'm not sure what that would be, so I'm curious.

I'm curious to know why you would run without an anti-siphon valve?

The bog is immediate and the popping is at high rpm. The popping isn't nearly as bad as last summer. It'll go just about full throttle with no issues. It's just that last little bit of throttle. The secondaires open straight up and down at full throttle. The primaries don't fully open. When you nail it, the secodnaries do open, but if you push the throttle quickly to the end you get a bog. Pull back a hair and it's runs good. No popping when you pull back a hair.

If we hadn't picked up this NOS Carter, which appears to be exactly like an Edelbrock, we would have gone with a Holley. Paul at the Chris Craft Commander site which has more marine 427 Ford info than anyone, loves the AFBs on these engines, although they typically push bigger boats and at lower rpms.

The jets and metering rods were changed to 427 specs, which were very close to what was there. The floats were adjusted as they were set too low. The accel pump is set for the biggest shot. I don't know about the springs.

We're going to put a straight nipple on and we should probably just swap the carb as it sounds like you guys think it is not likely the anti syphon valve.

A Holley wouldn't be easy, but we have 2 AFBs, one thats practically new and on the classic that we know runs good. The other is a fresh rebuild that hasn't been used. We've eliminated everything but anti symphon valve and the carb. When I found out we had the wrong anti symphony valve on there, I thought we'd do a test run first with the current carb before we switched it out. I just got an email from moeller and they say to use 30 cal for 200 hp and less. 15 cal for 210 hp and up. I hear some people use straight nipples which I may try first. The hesitation and popping are immediate though.

Pete, the flow rate must be based upon the resistance of the spring as there is a number on the side of the valve. Most I have seen are 30, although I've also seen 15 and 10. The unit of measurement is CAL. The lower the number, the more resistance to the spring. There is no chart or instructions as to what number corresponds with certain horsepower either in the labeling or on Moeller's web site. I went to our local marine store and they had 15s and 30s and no one could tell me the difference. I stopped at West Marine and they had 30s manufactured by Attwood. The clerk called Attwood and they didn't know what the number meant. We're trouble shooting WOT lean fuel condition, so for now I'm going to use a straight nipple to see if that is the culprit. I was curious if anyone was using a 30 CAL anti syphon valve on bigger engines with no problems.

Anyone have any experience with Moeller anti syphon valves? The aluminum ones are available everywhere and the brass ones not so much. I have found some sites that have both and say that aluminum is for less than 200 hp and brass for more than 200 hp. Anyone using the aluminum anti syphon valves on 300 hp and up engines?