Mercruiser 4.3 Surging at WOT - Aniti-siphon valve

BillK2632

Well-Known Member
SILVER Sponsor
Jun 25, 2009
2,899
Lake Norman, NC
Boat Info
2014 Cobalt R5
Engines
Volvo Penta V8-300 DPS
So I have been trying to figure out this surging problem that has developed this year. Boat runs great except at WOT, over about 4000rpm it will surge like it's starving for fuel. Not bad, would still reach WOT rpm of 4800. Today I decided to go through the entire fuel system:

Carburetor clean.
Fuel filter new this season.
Accelerator pump dumping fuel.
Carb inlet filter clean.
Fuel pickup clean.
Anti siphon valve working -- NO!

Anti siphon valve seems too tight, I can move the ball valve by pushing it with a screwdrive, but if I try to blow through it, I can't. Cleaned it out, same thing. I put a straight through connector on it and walah! Engine runs smooth all the way to WOT not surging at all.

I know people are going to say it's against coast guard regulation to remove it - and it is kinda. The regulation says you need a anti-siphon valve OR the fuel line must be above the top of the fuel tank. My line runs up from the fuel tank to the fuel filter and never dips below the top of the tank. Anyhow, still think I am going to replace the anti-siphon value, just have the straight through connector on for testing.

Anyhow, glad that is fixed, had been driving me a little nuts.
 
Awesome to hear it. Fuel issues seem to be this years gremlins. Had same kinda thing but ended up being rust in lines and weak fuel pump. That valve was the 64th thing i checked on my WOT problem
 
Good deal Bill...glad you figured it out.....

cliff
 

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