Primer Bulb–Reverse Flow, Losing Prime

[Jason2tpa]

Brief backstory: I recently installed a new fuel tank and fuel lines. Prior to this installation, when I go to prime the engine for the first ignition of the day the bulb is always empty. I've heard from others that their bulb remains full, or at least not completely empty. Since installing the new tank it's taken a lot more squeezing of the bulb to prime, maybe a dozen or so squeezes before bulb begins to fill.

Today was different. I would squeeze the bulb until my forearms were on fire, still no fuel. Eventually for some reason it began to fill, but moments later the fuel would reverse and the bulb emptied. Bad primer bulb?...sure, probably. I bought a new primer bulb, installed. I experienced the same issue. Kept squeezing till it eventually filled. This took about 2-3 minutes of squeezing to fully prime.

Dropped the boat in the water, started, all good. Ran the boat around for an hour or so. Stopping every so often, shutting down, and checking the bulb. During this time the bulb would remain partially full, which is normal.

No fuel leaks anywhere, plenty of fuel in tank, fuel pump functioning properly. Few questions:

* Primer bulbs have check valves, right? They prevent fuel from reversing flow. If this is correct, and the primer bulb is new....what's happening here?

* Fuel pump....are there also check valves in the fuel pump that prevent reversed flow from carb bowls?

* Even though the fuel lines are new, IF there was a puncture in the fuel line between bulb and tank, thereby pulling air instead of fuel, I would notice this fuel leak as it flowed into my bilge. So i'm really at a loss for what's happening, why it takes so many squeezes of the bulb. I had to look at the fuel gauge a few times because it seemed as if the tank was empty. Your thoughts on possible causes and what to look for?

* There seems to be debate on whether the fuel/water separator should be located between the tank and bulb or between the bulb and engine. If someone knows the definitive answer to appropriate location, please reply and detail its reasoning for location.

[amahaork]

Are you sure you not installed bulb in vent instead of pick up?

[Jason2tpa]

Are you sure you not installed bulb in vent instead of pick up?

I'm not following you ^^^. Bulb in vent?

[amahaork]

You connected something wrong. All simple really. Fill hose, vent hose, pick up tube, valve, filter, bulb, engine. Somwhere is air leak.

[Sequoiha]

I know it seems simple enough, but are you holding the bulb with the arrow pointing up, like toward the sky, the check valve in the bulb works with gravity. And not very well on its side.

[fairdeal]

here's a very good video on the primer bulb

https://youtu.be/Mrt38-ulYFc

and yes, a (mechanical) fuel pump is exactly analogous -
an inlet check valve, an outlet check valve, and the diaphragm is the "bulb"

[Jason2tpa]

You connected something wrong. All simple really. Fill hose, vent hose, pick up tube, valve, filter, bulb, engine. Somwhere is air leak.

All lines are connected correctly

[Jason2tpa]

I know it seems simple enough, but are you holding the bulb with the arrow pointing up, like toward the sky, the check valve in the bulb works with gravity. And not very well on its side.

Arrow on bulb points towards engine and is positioned vertically.

[fairdeal]

* Even though the fuel lines are new, IF there was a puncture in the fuel line between bulb and tank, thereby pulling air instead of fuel, I would notice this fuel leak as it flowed into my bilge.

not so. The fuel line system between tank and the bulb is never under pressure, and under "vacuum" when you are pumping the bulb.
Its entirely possible to have a leak which lets air in while pumping the bulb but never lets fuel out

* There seems to be debate on whether the fuel/water separator should be located between the tank and bulb or between the bulb and engine. If someone knows the definitive answer to appropriate location, please reply and detail its reasoning for location.

it makes absolutely no difference except for the first time you prime the system after changing the filter.
At that point the filter is empty of fuel but full of air.

since the primer bulb is much better at pumping liquid that at pumping air -
it it easier to have the bulb pumping fuel into the filter - pushing the air ahead
than have it trying to suck air out of the filter

[TownsendsFJR1300]

since the primer bulb is much better at pumping liquid that at pumping air -
it it easier to have the bulb pumping fuel into the filter - pushing the air ahead than have it trying to suck air out of the filter

Agreed with fairdeal 100% however I have my primer bulb AFTER the transom filter. Just worked out that way BUT with the transom filter there, it won't suck dry just sitting. And your ONLY priming from THAT FILTER..(as long as everything is sealed properly)

If I get a half pump (VST, after sitting for several weeks it's ALOT) And that's with the bulb laying on it's side(due to room constrictions).

Usually, (I have several spare bulbs for garage use), the primer bulb works BEST once it gets "wet" with fuel too.

I'd add that I last replaced my primer bulb with a genuine Yamaha bulb. The difference in the quality (and $)
was definitely obvious. Might be as simple as the bulb.

Perhaps pull the bulb, hook up to a line (apart from the boat), prime and see if it HOLDS FLUID (pointed upwards).

BTW, the carbs should not suck dry and actually could only "suck dry" to the needle seat. After that its sucking air and they'll still be fuel in the float bowl...

[Jason2tpa]

The primer bulb is new so let's assume it's functioning properly. If I'm having to squeeze bulb 50x to pull fuel into bulb, ones left to predict there is air being pulled into fuel pickup line.

The fuel pickup line was pushed over the barbs of the tanks 90° fitting and secured using a hose clamp. Sealant was used over the area where the 90° brass fitting screws into tank. There are no sharp edges or areas between the 90° fitting and bulb where the fuel pickup could be punctured. There are hose clamps on either side of primer bulb. I mention all of the above to imply the unlikely probability there could be an air leak from tank to bulb. Yet wouldn't there have to be if im having problems priming?

As I stated in my initial post, there is no fuel leak from bulb to engine. Which leads me to conclude an air leak exists from tank to bulb. But the task of visualizing the fuel pickup line and its connection to the tank is a laborious task. I'd have to remove center console and unseal hatch. So I want to be sure I've checked everything else before having to do this.

[99yam40]

Does your set up have an anti siphon valve?
could it be restricting the sucking of fuel?

does the valve leak back causing the fuel to leave where it should stay?

should the check valves in bulb keep the fuel from draining back to tank?

Take the bulb loose and see if it sucks as it should.
see if the valve in it work properly
test the anti siphon valve.
temperately hook up a clear tubing at the fuel pump to look for bubbles

[Jason2tpa]

Does your set up have an anti siphon valve?
could it be restricting the sucking of fuel?

does the valve leak back causing the fuel to leave where it should stay?

should the check valves in bulb keep the fuel from draining back to tank?

Take the bulb loose and see if it sucks as it should.
see if the valve in it work properly
test the anti siphon valve.
temperately hook up a clear tubing at the fuel pump to look for bubbles

Re: Anti siphon valve– if this valve is installed within the tank's brass fitting....No, there is not an anti siphon valve. When I installed the new tank I also had to install a brass 90º fitting. It was not included with the tank. This fitting is just a standard brass 90º, not specifically used for fuel marine applications.

Once I got the bulb full and tight I kept my hand loosely around it. Moments later I could feel the bulb expand at once. I'd then squeeze the bulb and it was no longer tight. This was done while engine was off.

If the fuel line/bulb system were functioning properly and you primed the carbs and the bulb was firm, but did not start the engine, the bulb should remain firm. Correct?

If so, and I'm able to feel the bulb expand after priming to tight bulb, fuel is reversing flow, right? But how is this possible if the bulb's engine side check valve is closed?

[pstephens46]

I would think it was expanding , filling with fuel from the tank side.

I never touch mine. Well almost never. I did use it to fill the vst after service. That's it. I fill my new separator with fuel prior to screwing it
on.

And it's not vertically mounted either!

Lightning may strike at any time. I'm going inside....

[Jason2tpa]

I would think it was expanding , filling with fuel from the tank side...

The bulb would expand AFTER I've primed bulb to firm. I just kept my hand loosely around bulb. So if the engine is off, thus fuel pump is off, the bulb could not expand with fuel from tank....fuel would have to reverse flow.