# Another Anti Siphon Valve Problem?



## jking (Aug 11, 2011)

Just rigged my boat project with a 90 Yamaha 2 stroke, before rigging, drained the tank, inspected it through the gauge opening - looked OK, replaced the fuel/water separator, new 3/8 fuel line from the fuel connection in the motor well to the motor (there's a through the glass aluminum nipple at the well), new clamps, new Yamaha ball, arrow facing in the direction of the motor, new Yamaha fuel connection at the motor. Didn't replace the fuel line from the tank to the connection through the motor well, no evidence of leaking in the lower bilge. 

Ball will pump firm, motor starts fine, great hole shot, take off will run wide open then fuel starve. Shut the motor down, re-pump the ball, same thing will take off run some and fuel starve.

If I come off the throttle as it starves out it and don't run it completely out of gas it will still run sometimes but rough idle fuel starved, same as when it's just running out of gas normally if I run the gas out after use at home.

I also think when I first started it at the ramp it was fuel starved on idle, idling a little rough , then evened out idling out to deeper water.

Hull is an 1985 with a built in 12 or 15 gal aluminum tank sealed in the seat bench. Anything I should check or procedure I should do before I cut into the glass to get to the feed area of the tank to check out the anti siphon valve? or is this a good bet that's what it is?

Sucks, I had just hit 5500 RPM passing 45 MPH trimming up before it shut down, really wanted to she what she would do. I believe that's about top end but I had just gotten there, damn! 

Any help is appreciated


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## tortuga (Oct 12, 2008)

First run using a small portable gas tank. Even a jerry jug. That will tell you if there is a problem ahead of fuel line. Also install new fuel line old ones can swell up and the inside diameter gets reak small. The ball will flatten if there is a restriction at anti siphon . Also if you run boat and pump the ball and she keeos running then yiu have a bad fuel pump diaphram.


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## jking (Aug 11, 2011)

Ball is pretty much collapsed, not pancaked, but not right when it happens. If I keep it running at idle after starvation and try to pump the ball it really won't come back firm and I can't get enough gas too it that way to get it un-starved. Shut it off for 10 -15 seconds and pump the ball while it's off and ball will pump right up firm again in a few pumps, no delay. Will run right and fuel starve out again.


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## DrG (Apr 19, 2012)

Some newer vintage two part fuel lines (inner lining and outer casings) are not maintaining their integrity -- the inner lining is seperating from the outer casing and collapsing inside the fuel line. It cannot be seen with the naked eye. The earlier suggestion to hookup a jerry can at the motor will determine if you are experiencing a fuel restriction upstream of the motor. If you are, you will have isolated it to just a few things that could be going wrong on the fuel delivery side.


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## swaddict (Dec 19, 2009)

sounds like fuel pump


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## jking (Aug 11, 2011)

Wanted to add this is the second wet test. First time I went out and the motor ran fine up to about 4500 rpm topped out, around 35 mph. Did a bunch of hole shot tests, ran it up to wide open, starts and stops and running for about 30 minutes. Picked up the family and motored around mid range rpms and idling for about an hour.

Running on plane on the way back that first trip was the first time it starved all the way out, idled in keeping it running pumping a semi collapsed ball occasionally to keep it idling.

Found the cheap fuel line setup from the well to the motor had the liner collapsing in it and restrictions at the connections. Replaced everything from there to the motor with 3/8 line and new Yamaha parts.

I believe that change out allowed it to run up to 5500 rpms with the increased speed numbers before it starved out again.

I'm guess I'm investing in spare tank for testing. Replacing the feed line to the motor well could be a major operation on this boat the way it's run with no access to it.


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## jking (Aug 11, 2011)

Update.

Ran on a an auxillary jerrican and the motor did not fuel starve, ran about 3 gallons through the motor testing it off the jerrican.

Went to the dock switched back over to the main tank and couldn't get it to fuel starve again the way it was doing before. Ran exactly like it did on the jerrican. Did a variety of tests over about an hour, idling for a while then take off, shut down for a while and restart, hole shots, etc.

Also I couldn't get it to run over 5200 rpm on either the can or the main tank. I know it had hit 5500 the previous run before it fuel starved.

Suggestions? I'd like to think it magically fixed itself but I know it rarely works that way.


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## Creek Runner (Sep 1, 2011)

> First run using a small portable gas tank. Even a jerry jug. That will tell you if there is a problem ahead of fuel line.  Also install new fuel line old ones can swell up and the inside diameter gets reak small. The ball will flatten if there is a restriction at anti siphon . Also if you run boat and pump the ball and she keeos running then yiu have a bad fuel pump diaphram.


^this,

fuel pump test remove the 2 10mm bolts that hold the fuel pump to the engine block, leave everything else connected. Pump the primer ball and if gas squirts out of the back of fuel pump, you have a bad fuel pump. I have stated these instructions over and over again needs to be a sticky mods!

If the motor isn't acting up now then I would say you had a bad A/S valve. They can work and not work until they finally fail. The 5200 vs 5500 is probably due to load, tide, wind, etc. 

question: I saw this was a project boat for you, how long did that Yamaha sit with out running? If it was more than 90 days hope you did a carb job, before running her.


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## jking (Aug 11, 2011)

The fuel pump test failed, pulled it off, pumped the ball and sure enough there's gas pouring out of the back of it.

Creek, didn't rebuild the carbs, I was told by the previous owner of the motor that it had a recent carb rebuild. 

Really appreciate the guidance. You think I should go through the carbs if it's running right following the fuel pump change?


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## tortuga (Oct 12, 2008)

if it runs good don't worry about the carburetors


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## jking (Aug 11, 2011)

Just to close this out, ran it again with the new fuel pump and it fuel starved.

Knowing now there's nothing left but the tank and the feed line to the well connection I put her under the knife to get to the tank feed area. 

Turns out the feed line from the tank was mush, I honestly can't believe it ran at all.

Pulled the feed tube out of the tank and it turns out there is no anti siphon valve in this tank from 1985, just the fluted end of the pickup tube. 

So as it turns out just about every part of the fuel feed system was bad and needed to be replaced.


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