Anti-Siphon Valve Location? '96 Chaparral 1935SS

vzett

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I'm trying to run-down some erratic engine behavior with my '96 Chap 1935SS Cuddy. Engine is 4.3L Merc with 4 brrl Weber. I'm leaning towards a problem in the fuel system and want to eliminate the anti-siphon valve as a possible cuplrit, but I'm not sure where it's located in relation to (on in) my fuel tank. <br /><br />The fuel line exits the tank through what appears to be an L-shaped steel fitting secured to a threaded collar in the tank with lots of pipe sealer. Is the A-S valve likely somewhere below the collar inline with the feed straw?<br /><br />Thanks,<br />vzett
 

Bondo

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Re: Anti-Siphon Valve Location? '96 Chaparral 1935SS

an L-shaped steel fitting
That Should be your anti-siphon valve..........<br /><br />It's inside the Hose Barb.......
 

Chris1956

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Re: Anti-Siphon Valve Location? '96 Chaparral 1935SS

Vzett, The antisiphon valve on my SeaRay was located on the fuel tank's fuel pickup, at the top of the fuel tube, next to the L-shaped fitting. It was hidden under the fuel pickup tube, which unscrewed from the L-shaped fitting.
 

TilliamWe

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Re: Anti-Siphon Valve Location? '96 Chaparral 1935SS

quote:<br />--------------------------------------------------------------------------------<br />an L-shaped steel fitting <br />--------------------------------------------------------------------------------<br /><br />That Should be your anti-siphon valve..........<br /><br />It's inside the Hose Barb.......
I agree. take the fuel line off that fitting, and there should be a graduated fitting that stuck into the hose, and the other end threads into the "L-shaped" fitting. Unscrew it from that "L-Shaped" fitting and that should be the anti siphon valve in your hand.
 

vzett

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Re: Anti-Siphon Valve Location? '96 Chaparral 1935SS

Thanks for the good advice. I did have some debris trapped at the intake end of the A-S valve although the valve and spring were clean. Not sure the debris was enough to be causing my RPM fluctation, but certainly good to remove. <br /><br />Fortunately, the access panel on my boat is correctly placed and future inspection/cleanings will be pretty easy.<br /><br />- vzett
 

Don S

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Re: Anti-Siphon Valve Location? '96 Chaparral 1935SS

Not sure the debris was enough to be causing my RPM fluctation, but certainly good to remove. <br />
Ahh, now that we know that you have a problem, maybe you can get some answers. You may have air leaks (That don't leak gas) between the tank and the fuel pump causing air in the system. It's very common. Just put a clear hose between the fuel pump and the hose from the tank and look for air bubbles while running under load. In neutral probably won't show it.<br />Also check the fuel tank vent. A partially plugged vent can also cause the problem.<br />If it looks ok, just pull the fuel fill cap off while running under load and see if it makes a difference.
 

vzett

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Re: Anti-Siphon Valve Location? '96 Chaparral 1935SS

Don,<br />Thanks for the hints. Here's a break-down of the problem and my trouble-shooting so far. I have 2 primary symptoms which I'm not sure are the same problem, but could be related. Engine is a 4.3L Merc LHX+ (4bbl weber)<br /><br />1. RPM fluctuation under load<br />- this started about 3 months ago<br />- most common at 2000 - 3500 RPM<br />- engine would gain 200-400 RPM in "real" power randomly without a change in throttle position, sometimes would stay, sometimes would drift back down<br />- seemed worst in rough water, but given its randomness I wouldn't stake too much on this<br />- inspected ignition system and replaced worn wires, cap, and rotor (plugs are new as of last summer)<br />- idle RPM jumped 300RPM since replacing all the ignition components, last test run was flawless in terms of RPM fluctuation, but I'll wait to declare victory<br /><br />2. Sudden engine stoppage w/o warning<br />- 1st happened 4 months ago returning from a normal run, engine just died at cruise on plan, restarted immediately, couldn't reproduce problem<br />- 2nd and 3rd occurance last month, same situation running normally and engine dies, restarts immediately, happened twice in quick succession then no problem. That day I also had significant problems with RPM fluctuation and very rough water (which made for a stressful day since the engine quit 4 miles out from land in any direction)<br />- 4th occurance after last test run with no RPM problems, was flushing at idle and engine quit, would restart for .5-1s then quit again, left overnight and started and ran normally prior to cleaning the A-S valve today.<br /><br />#2 seems to clearly be a fuel system problem. I've purchased a spare oil pressure switch as I've heard these can partially fail and cause intermitent headaches. It could conceivably be causing #1 by underfilling the carb under load. Of course, it could also be a failing fuel pump, air in the lines, blocked vent, etc... I'm glad I can do the work myself, I'd hate to think what my labor bill would be otherwise. It'll be nice to have it back running well.<br /><br />- Virgil
 

TilliamWe

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Re: Anti-Siphon Valve Location? '96 Chaparral 1935SS

Virgil, that bit of debris in that valve can cause a lot of the symptoms you described. We had a similiar problem on a 1983 Renken, and it would idle, but just could not get enough fuel to run faster than about 3000rpm. Unfortunately for us, we had to cut out a portion of the deck, under the engine cover, to remove the tank, in order to get to that fitting. Turns out it had those "helicopters" from maple trees in there!<br />Cross your fingers, but I think you found your problem!<br /><br />Merry Christmas.
 

highaltitude

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Re: Anti-Siphon Valve Location? '96 Chaparral 1935SS

don s. is correct about diagnosing the problem with a clear fuel hose. the problem is going to be in the fuel pump or downstream. i have seen a bad fuel pump (mechanical or electric) cause similar problems. very difficult to diagnose.
 

vzett

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Re: Anti-Siphon Valve Location? '96 Chaparral 1935SS

I've put about 3 hours and 2 launches on the boat since removing the debris with no problems thus far.<br /><br />Before the last trip, I went ahead and adjusted the idle down a bit and leaned the idle mixture a tad. Engine seems much smoother at low RPM now and idles in gear 700-800 which provides good finese for docking.<br /><br />- Virgil
 

TilliamWe

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Re: Anti-Siphon Valve Location? '96 Chaparral 1935SS

Virgil,<br /><br />So it was "just" the dirt in the anit-siphon valve then?
 

vzett

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Re: Anti-Siphon Valve Location? '96 Chaparral 1935SS

Well, so far so good. I'm reluctant to declare victory until I have a few more uneventful days on the water, but it appears the problem has dissappeared.<br /><br />- Virgil
 

pine island fred

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Re: Anti-Siphon Valve Location? '96 Chaparral 1935SS

if you have further problems, remove the fuel pick up tube in the tank again.look down the tube and you will find a screen finger filter in the tube. i seem to remember it being installed from the top, you can push it out from the bottom. if you had debris on the a/s valve this filter is sure to have trash on it. causes problems like the old G.M. tea bag in the gas tank. regards fred
 

vzett

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Re: Anti-Siphon Valve Location? '96 Chaparral 1935SS

thanks for all the good advice.<br /><br />We trailered up to Lake Seminole for MLK day and spent about 3 hours on the water. Still running great without any problems. 1st time on a man-made lake with so many snags at or above the water. Needless to say, we stayed in the marked channels.<br /><br />It was fun being one of the larger boats on the water for a change.
 

Buttanic

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Re: Anti-Siphon Valve Location? '96 Chaparral 1935SS

Make sure your fuel tank vent has a screen on it. There is an insect that will build a mud nest in any small hole it finds and plug it solid. I have had them plug my vent and also the outlet on fire extinguishers. Now I keep a foam ear plug in the fire extinguisher nozzel to keep them out.
 
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