Primer Bulb Explained

[panasonic]

This little device seems to come up here quite often. I think a lot of people don't know how they work, or the trouble it can cause when it does not work properly.


https://youtu.be/Mrt38-ulYFc

[boscoe99]

Some primer balls don't use springs. They might use a flapper valve. All the more reason to hold the primer ball vertical when using it, with the discharge port on top. Gravity will help the valves do their job.

Another tip is that primer balls force gasoline outward much better than they draw air inward. This is one of the reasons for having the primer ball between the tank and the Racor fuel filter so that it always remains full of gasoline and can push that gasoline into the Racor to refill it when a new element is installed. If downstream from the Racor it can be a challenge for the primer ball to pull all of the air out of the Racor so that gasoline can flow inward.

[fairdeal]

Saw an interesting thread on THT a few days ago - a poster had an old carbureted Yamaha (OX66?) with a hot restart problem and thought the cause might be his primer bulb.

It was confirmed to him by others that yes, not keeping the bulb vertical would "allow the fuel to run out of the engine and back to the tank".

It was not mentioned if that model has any sort of fuel pump with integral check valves.
Or exactly how the fuel already in the carburetor bowls gets sucked back out...

[99yam40]

lots of sharp people over there posting

[pstephens46]

Am I supposed to remount the primer bulb to be vertical?
It has worked fine for 5 years horizontally. I only used it once to fill vst. I fill my new fuel separators with gas prior to screwing them on.

[fairdeal]

Am I supposed to remount the primer bulb to be vertical?

if you want to be a faithful THT reader, yes.

And whatever you do, don't put dielectric grease anywhere near your electric connectors - "its an insulator"

Of course, make sure you replace all your batteries at the same time - with the same brand - and never "mix types"!

[boscoe99]

Am I supposed to remount the primer bulb to be vertical?
It has worked fine for 5 years horizontally. I only used it once to fill vst. I fill my new fuel separators with gas prior to screwing them on.

It only matters when the ball is being pumped by hand. Does not matter when the ball is not being pumped.

[pstephens46]

if you want to be a faithful THT reader, yes.

And whatever you do, don't put dielectric grease anywhere near your electric connectors - "its an insulator"

Of course, make sure you replace all your batteries at the same time - with the same brand - and never "mix types"!

I was being sarcastic as usual. No plans to change anything regarding primer ball. I remember the old BajaKeith would rattle on page after page regarding primer and batteries.