Any ideas why my primer bulb looses pressure after about 5 mins?

A month ago I bought a "new to me" boat, first thing I did after test ride was pull the fuel tank and clean it out as it was full of crud. (see link below)

http://texasfishingforum.com/forums/ubbthreads.php/topics/10631757/Re:_Cleaning_Fuel_Tank#Post10631757

After installing the tank back into the boat I put 25 gallons of fuel in the 49 gal tank. I checked all of the hose clamp fittings and they are all tight. I replaced the inline filter/ water separator as well and it seems to be sealed tight.

I go out to the lake and prime the bulb until its firm and run around for a while and it runs great. If I stop to fish for 5 or more mins the bulb is flat again and I have to prime it back up.

Any ideas? I don't know if this was happening prior to purchasing the boat or not so ill consider checking anything that might be related.

It is most likely the bulb. I have gotten bad brand new ones before. A very small leak will do this also.

I was going to say the same thing bad bulb or your one of your horse has a small leak in it but i would replace the bulb first

I carry a spare bulb with me as I have had this happen while on the water easy to replace even on the water,but best if you can get to shore boat will be stable.

Had this happen. It was a small air leak at the bulb

If not the bulb, your low pressure fuel pumps on your engine may have a hole in the diaphram. Check the inside of your prop and see if it is sooted up.

If you replace the bulb, be sure to use a quality one (from Merc or Yamaha, etc)

The bulb when pumped lifts the fuel from the tank and temporarily pressurizes it forcing fuel and any air in the lines into the motor and its vapor sep tank and fuel lines.

Once the motor is run, the motor's fuel pump creates vacuum (lift) in the boats fuel lines to draw fuel up and into the motor...there is no longer any pressure in the bulb nor should there be after the motor is ran.

The bulb should remain reasonably full of fuel, but it will not be at pressure. The motors lift pump should be able to continue to draw fuel from the boat later in the day without further priming as the bulb should be remain reasonably full. If not you have air leaking/entering the fuel line or pump.

The OP said the bulb goes flat. That has to be a blockage in the fuel line between the tank and the bulb. I had the same problem with my new SeaArk. The fuel tank wasn't blocked on one end and it shifted over and pinched off the fuel hose.

? Kill your motor wait 5 minuets, unhook the motor side of the bulb and see what happens. You will get fuel sprayed on you from the pressure.

Replaced the bulb last night. Went out today. It ran good, bulb never went flat. Only primed it when I launched and never had to re-prim.

Thanks guys.