Primer bulb goes flat on WOT- question on fuel line!

[fish__bait]

Hi, reviewed past posts on this topic, rebuilt my fuel pump, replaced the 10 year old bulb with a new Moeller bulb, drained the poly tank did not see any debris from the little bit i could see through the sending unit opening, i know that does not say much. will remove the tank as last resort. Vent line is clear no dirt dobber nests found! Yes bulb is in proper flow direction. Is there supposed to be a check valve in the 90 degree fitting that connects the fuel line to the fuel hose? I have it apart and the pick up/screen is fine no signs of debris, but no spring/ball bearing as a check valve in it or the 3/8" barb fitting. Or is the only check valve needed the one in the primer ball? How likely is it i bought a bad ball? i have had this boat for 12 years. (Champion 18.4 with a Merc Black Max 150). I replaced the fuel hose last year with a 3/8" rubber gates fuel hose.....Also the screen in the fuel pump was fine - no signs of buildup or debris (fuel filter fine too-replaced as well)........So my real question(s) are;

1) Can there be enough vacuum that it would collapse a rubber hose thereby pulling primer ball flat? I noticed the marine hoses i have seen are a grey semi rigid material. My fuel pump is just a simple diaphragm pump.

2). As i mentioned previously i have had this boat for a lot of years....the manifold 90 at the tank does not have any internal check valve now and i have not had this problem ever before....is it supposed to be a check valve assembly?

3). Any thing i might have missed....It seems like i have narrowed it down to the rubber fuel line (hence the above question) or trash in the tank somehow.

Thanks for your time.

 

[Chris1956]

Re: Primer bulb goes flat on WOT- question on fuel line!

A collapsed fuel primer bulb means a restriction in the line upstream of the bulb. The tank vent thru hull, and vent hose are prime suspects, especially if there is no antisiphon valve in the fuel pickup elbow or tube. On my SeaRay, the antisiphon valve was under the fuel pickup tube. The tube would unscrew from the elbow.


Last summer my neighbor had the same issue you do. It turned out to be a clogged screen in the fuel vent thru-hull.

 

[fish__bait]

Re: Primer bulb goes flat on WOT- question on fuel line!

Thanks for the reply....i have checked the vent line and can blow easily through it back into the tank..........the tank is a son of a gun to take out and hard to reassembly vent line and fuel line to it from under the cap....which is my next thought. Tracker dealer will let me take the primper bulb back to exchange so i am gonna do that also even though i think buying a bad bulb is a long shot guess!

 

[j_martin]

Re: Primer bulb goes flat on WOT- question on fuel line!

That mota needs about 15 GPH of fuel flow at WOT. If the fuel line between the bulb and the tank is soft enough to collapse, and it does, that'll fold up the primer bulb in a heartbeat. Size matters here also, you need the larger diameter (3/8" I believe) to service a big engine.

The Mercury fuel line and primer bulb work just fine. A lot of the aftermarket stuff just can't cut the mustard.

Get it fixed before you melt down a piston or two. That'll happen in a New York Minute when you starve them for fuel.

hope it helps
john

 

[daveswaves]

Re: Primer bulb goes flat on WOT- question on fuel line!

You can try a run with the fuel cap off or loose to eliminate the vent line. I have also seen the fuel pick up suck in a plastic oil bottle seal. After the engine stops the seal drops and floats away to hide in the corner of the tank you cannot see.

 

[fish__bait]

Re: Primer bulb goes flat on WOT- question on fuel line!

Well I took it back out on the lake after again verifying the fuel line/primer bulb/pickup tube were clear and unobstructed. The new primer bulb has a very sensitive internal spring so i was confident it is not the culprit.

Once warmed up and at WOT i only went 1/4 mile before it bogged down again. When it stalled on me at the lake i immediately opened up the gas tank to see if it would break vacuum- and this made no change in inflating the flat primer bulb.

This time i took the fuel line off at the tank and put it into a seperate 2 1/2 gallon can. I was able to run full throttle without a miss or any problem for about 10 minute or so so i figured i narrowed it down to the tank. I went home pumped the gas out the tank/removed tank from boat and rinsed out several times with clean fuel. I strained all the fuel i poured out with a super fine mesh paint strainer and only pulled out a small piece of what looked like the remains of a wasp midsection. I was hoping to find something significant in the tank- so needless to say i am still dissapointed. If this happens again the only thing i haven't addressed is changing out the gates 3/8" fuel line with the Mercury semi rigid fuel line.

any other thoughts/ideas? I am hoping the small piece of matter removed was enough to get stuck on the pickup tube screen and/or in the process of rinsing out tank i broke any debris up enough prior to pouring through the strainer.

 

[j_martin]

Re: Primer bulb goes flat on WOT- question on fuel line!

Well I took it back out on the lake after again verifying the fuel line/primer bulb/pickup tube were clear and unobstructed. The new primer bulb has a very sensitive internal spring so i was confident it is not the culprit.

Once warmed up and at WOT i only went 1/4 mile before it bogged down again. When it stalled on me at the lake i immediately opened up the gas tank to see if it would break vacuum- and this made no change in inflating the flat primer bulb.

This time i took the fuel line off at the tank and put it into a seperate 2 1/2 gallon can. I was able to run full throttle without a miss or any problem for about 10 minute or so so i figured i narrowed it down to the tank. I went home pumped the gas out the tank/removed tank from boat and rinsed out several times with clean fuel. I strained all the fuel i poured out with a super fine mesh paint strainer and only pulled out a small piece of what looked like the remains of a wasp midsection. I was hoping to find something significant in the tank- so needless to say i am still dissapointed. If this happens again the only thing i haven't addressed is changing out the gates 3/8" fuel line with the Mercury semi rigid fuel line.

any other thoughts/ideas? I am hoping the small piece of matter removed was enough to get stuck on the pickup tube screen and/or in the process of rinsing out tank i broke any debris up enough prior to pouring through the strainer.

Did you pull the pickup tube and check out the screen on the end of it, and the check valve if it has one?

With our modern crappy fuel, sometimes there's a nearly transparent sludge formed that can plug up that fine screen very easily.

 

[CharlieB]

Re: Primer bulb goes flat on WOT- question on fuel line!

I still suspect that Gates fuel line from the tank to the primer bulb.

The softer the wall of the hose the easier it will suck shut.

Head, the elevation of the fuel level increases the vacuum required to pull the fuel, when you switched to the portable tank the 'Head' was less than when on the main tank, vacuum was reduced and the problem would not repeat.

Replace that length of fuel line with certified MARINE rated fuel hose.

 

[cbavier]

Re: Primer bulb goes flat on WOT- question on fuel line!

Could it possibly be a pin hole in the fuel line from the bulb to the engine?
Just my two cents.

 

[j_martin]

Re: Primer bulb goes flat on WOT- question on fuel line!

Could it possibly be a pin hole in the fuel line from the bulb to the engine?
Just my two cents.

Nope

 

[daveswaves]

Re: Primer bulb goes flat on WOT- question on fuel line!

There is still some unanswered questions on the table, did you remove the fuel pick up tube and clean it and the screen at the bottom? The wasp remains are enough to cause a problem, it does not take much. As Charlie B said, the 3/8 gates line is suspect as well.

 

[fish__bait]

Re: Primer bulb goes flat on WOT- question on fuel line!

I have pulled the pickup tube out (several times) and the screen is clean, no check valve also in the tee fitting. When i tried to pull vacuum on the hose/bulb from the tank side the bulb collapses before the fuel line. There are no cracks or pin holes in the tube or fuel line.

I have entertained the idea of the increased suction head from permanent tank to the portable on the deck but the difference is less than 5 inches. At roughly .43 psi difference per foot i think this would be negligable.

I guess by deduction the next thing to do would be change out the fuel line...

 

[daveswaves]

Re: Primer bulb goes flat on WOT- question on fuel line!

I have pulled the pickup tube out (several times) and the screen is clean, no check valve also in the tee fitting. When i tried to pull vacuum on the hose/bulb from the tank side the bulb collapses before the fuel line. There are no cracks or pin holes in the tube or fuel line.

I have entertained the idea of the increased suction head from permanent tank to the portable on the deck but the difference is less than 5 inches. At roughly .43 psi difference per foot i think this would be negligable.

I guess by deduction the next thing to do would be change out the fuel line...

I know you have pulled out the pickup tube before and I know the screen is clean, I don,t know that the tube itself is clean. Something is restricting the flow. It still could have been the wasp.

 

[j_martin]

Re: Primer bulb goes flat on WOT- question on fuel line!

I know you have pulled out the pickup tube before and I know the screen is clean, I don,t know that the tube itself is clean. Something is restricting the flow. It still could have been the wasp.

And like I said, it's a real fine screen, and I've seen them plugged with a semi-transparent material that is hard to see.

Another thing I've seen is an oil bottle seal in the gas tank, randomly sealing the end of the pickup tube.

Brings up another thought. Clearance between the pickup tube and the bottom, and possibly pulling up the flexible bottom and plugging the pickup. Most pickups are notched to prevent this, but bears checking.

 

[DJ]

Re: Primer bulb goes flat on WOT- question on fuel line!

A "flat" primer bulb is 100% fuel restriction.

 

[fish__bait]

Re: Primer bulb goes flat on WOT- question on fuel line!

Woo Hoo.....i do believe it must have been debris in the tank. I took it back out yesterday after putting tank back in and bolting everything back up. I ran it all afternoon (used about 12 gallons of gas) and the motor ran great, never a hesitation nor a stall.

Thanks for all the input fellows!

Have a great Thanksgiving- God Bless ya'll!

Kirk

 

[Capt.Riz]

Re: Primer bulb goes flat on WOT- question on fuel line!

i've had the same problem with my 87' 50hp BM. I noticed that sometimes when i put the cowling back on it would pinch the fuel line, since mine (and maybe yours ) is a split cowling it could be the same problem, it won't help to just take a minute and check it out!

Smooth Sailing

Capt. Riz