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The fuel demand valve is needed with the new carb rated portable tanks. With the new tanks the fuel cap provides for pressurization of the tank to prevent from releasing volatilized gasoline into the atmosphere. Without the the fuel demand valve pressurized fuel is transmitted to the engine. This will cause flooding in the instance of carbureted engines. The fuel demand valve is a pressure drop regular. I had one installed on my Sport 15 without problems until I removed it when I recently installed my new custom aluminum tank.
Finnegan wrote:
Who wants bulged-out, pressurized tanks on a your boat on a sunny day? It sounds to me like the solution is to put a conventional vent-screw cap on a new tank. The whole situation sounds like trying to kill an elephant with a BB gun.
Agree - once can convert the carb rated tank to a standard one by switching to a standard vented cap.
Thanks, the vacuum restriction of the Attwood FDV says less than 2kPa (0.29 PSI). I don't know if that is significant with an older Mercury 90hp fuel pump or not. I'm mainly concerned about a pressure drop and restricted flow.
Sorry to resurrect an ancient thread, but I wanted to let everyone know that these can indeed cause vacuum locks. I have a 2014 Dauntless 170 with a 90hp Mercuriy. The boat is equipped with an IDFV (integrated fuel demand valve) on my fuel tank. I have been experiencing RPM drops after about a half hour of running the boat. Shortly after this, the motor will die and become unable to restart.
I suspected the IFDV and ordered one as a replacement (actually kind of difficult to find the correct one. Mine is an Atwood 99ifdv00-1) Every time I took a technician to the boat or tried to recreate the issue, I couldn't (figures.) I figured it was just related to the hot weather in summer causing the tank to swell.
Well, today (December 14th) when I took the boat out, it happened again where I lost RPMs, the motor died and I could not restart the motor. It acts like the fuel pump is bad and there is no prime to the fuel system. The motor will turn over but never fire up.
I popped the fuel cap open today out of curiosity and immediately all the pressure released from the tank. I went to start the motor and it started right up with no issues. I had to take the boat back into the marina with the fuel cap open the entire time.
I'll be replacing the fuel demand valve before going out again.
