Losing fuel prime at low speeds

[scottsdale816]

I have a 2004 Mercury 50 hp (ot811232) that runs great when running past 1000 rpm but anything below that it looses fuel prime, the ball goes soft, I have rebuilt carburetors, rebuilt fuel pump, changed primer ball, did away with quick connect fuel coupling, increased vacuum hoses size to 1/4. Checked ports for vacuum. While going slow it will start to run out of gas, you can pump primer ball and it will continue to run. If running over 1000 rpm it will run all day and never lose prime. I have been tempted to install a low pressure fuel pump in between the tank and primer ball that would keep the ball fuel at all times but don’t want to cause a flooding issue. Any ideas??

[JOE54]

oem bulb and pump kit ????

[scottsdale816]

Not oem bulb but has done it with 2 different bulbs, went through fuel pump and rebuilt it.

oem bulb and pump kit ????

[Rip Bass]

If you bought an Attwood bulb from Walmart you should trash it and get a Mercury bulb.

[scottsdale816]

Has mercury bulb on it now and is still doing the same thing, runs all day long at above 3000 rpm but when trying to idle through a no wake zone will constantly shut off and must reprime the bulb.

[JOE54]

check for and remove anti syphon valve in tank fitting, did you use mercury fuel pump kit from merc marine theres a difference

[scottsdale816]

check for and remove anti syphon valve in tank fitting, did you use mercury fuel pump kit from merc marine theres a difference

I used a Sierra kit for the fuel pump. Where would I find anti syphon valve located at?

[JOE54]

fitting where fuel line connects, would get oem pump kit

[scottsdale816]

fitting where fuel line connects, would get oem pump kit

What is the difference between pump kits? just curious?

[JOE54]

diaphram thickness and check valve material,diaph too stiff mostly

[silvertalon]

I agree quicksilver parts are the best but, I use Sierra pump kits every day and have never had a problem. Maybe just luck. You must try a remote shop tank to eliminate your tank vent and feed system. This will also verify your fuel line and pump function.