What causes fuel to go back into tank after primin

[tony08]

What causes fuel to go back into tank after priming. Have changed backflow 3 times and bubble twice.

 

[cyclops222]

Should be bad check valves in the squeeze Primer Bulb.
Unscrew the fuel tank filler cap to release any excess ...VACUUM....in the tank.

 

[alldodge]

Is this an OB, and if so what is the problem?

 

[tony08]

Should be bad check valves in the squeeze Primer Bulb.
Unscrew the fuel tank filler cap to release any excess ...VACUUM....in the tank.

Tried with cap off with same results

 

[tony08]

Is this an OB, and if so what is the problem?

Evinrude 88 spl. Fuel going back into tank after priming.new check valve and primer.

 

[alldodge]

Need a OB guy, don't know if tank has a check antisiphon valve of some sort

 

[tony08]

Need a OB guy, don't know if tank has a check antisiphon valve of some sort

It does. 3rd new one tried. Same results.

 

[cyclops222]

Would leaving the cap loose relieve the problem ?
A few million defective parts ?

 

[racerone]

The primer bulb is a simple manual pump.----Once it is used to fill the carburetor it does nothing !----Going soft after filling carburetors means nothing.

 

[dingbat]

You need an opening to atmosphere (leak) to break the vacuum of a sealed fuel line to allow the fuel to drain back.

A sticking float valve would do it, as would a leaky fuel fitting. Fuel filters and band style hose clamps are another common source of vacuum leaks.

FWIW: a vacuum leak doesn’t necessarily leak fuel

 

[cyclops222]

Good primer bulbs ... ONLY... pump gasoline in 1 direction. The built in check valve must prevent drain back. How else will the pump ...HOLD ...2 to 5 pounds of pressure in the carburetor FLOAT needle valve system.
My primer bulb has ROCK HARD shape a couple of days later. I DO NOT need to squeeze it at all.
Yes there really can be 3 million REJECT squeeze primer bulbs out there.

 

[cyclops222]

Think about a Primer bulb FUNCTION.
EACH squeeze is...SUPPOSED.... to INCREASE the fuel pressure in a carburetor float level that is several feet HIGHER. Than the gas level in a near empty gas tank on the floor under it. A soft bulb just does NOTHING to fill the carburetor to operating pressure.
3 million rejects and counting.

 

[cyclops222]

This spring I finally changed the primer bulb for the generator. It was just to hard to squeeze efficiently. about 35 years old. Still pumped . But caused cramped muscles in my hand.

 

[racerone]

The bulb fills the carburetor float bowl to the correct level.-----The fuel in the float bowl is exposed to atmospheric pressure.-----Once carburetor float bowls are full the bulb does nothing.

 

[cyclops222]

Some times I disconnect the hose connector at the engine and allow the carburator & pump to go dry. I then use the bulb to recharge the carburetor completely. Instead of a long dry cranking of the engine.
Reconnect connectors. 1 squeeze or 2 and engine is running with just a 1/4 of a second of starter cranking.

 

[flyingscott]

Think about a Primer bulb FUNCTION.
EACH squeeze is...SUPPOSED.... to INCREASE the fuel pressure in a carburetor float level that is several feet HIGHER. Than the gas level in a near empty gas tank on the floor under it. A soft bulb just does NOTHING to fill the carburetor to operating pressure.
3 million rejects and counting.

no it doesnt. That is not even close to true

 

[flyingscott]

Good primer bulbs ... ONLY... pump gasoline in 1 direction. The built in check valve must prevent drain back. How else will the pump ...HOLD ...2 to 5 pounds of pressure in the carburetor FLOAT needle valve system.
My primer bulb has ROCK HARD shape a couple of days later. I DO NOT need to squeeze it at all.
Yes there really can be 3 million REJECT squeeze primer bulbs out there.

Your bulb should not be hard after days. if it is the tank vent is suspect,

 

[racerone]

The primer bulb does NOT pressurize fuel in the carburetor bowl!!

 

[cyclops222]

I always leave the tank filler cap loose. To prevent any possible high vacuum or overpressure of the pump or rubber tipped float pin.

 

[Tassie 1]

Dosen't answer your question but l bought a new primer and line a few months ago.
Wouldn't prime straight out of the packaging,

Luckily l had bought it locally...only a couple of mins drive.

Mechanic tested it on his system and it was faulty.
Replaced it.
Said it had probably been sitting on his shelf for 3 years.