The primer bulb or your tank vent probably isn’t working.

 

Tank not venting, did you try running with the cap loose or off?

 

Same gas tank that I used on the Spear without an issue so the tanks out and brand new industrial gas line so I am pretty sure that's out also.

 

Did you try? Wouldn’t rule it out until you did. Then you could be sure.

 

It's definitely not the tank as it was used on another boat without a issue and the gas line is brand new 3/8 tubing fresh fittings on tank and motor so I am at a loss as to the issue.

 

I would try the tank connection as well as what others said with the vent. I know its never failed you before but things do happen. I bought a new fuel connector for my old boat and I found out it wasnt seating properly after a similar issue.

 

I will check just weird to never have an issue with any other boat I am contemplating my Mercury 25 I know that'll pull the gas back for sure.

 

Like others have said... its either the tank is not open on the vent, or bad primer bulb or connection of the hose to tank or motor could also fail. It's not the engine based off what I've seen if primer bulb is going flat after a few minutes of running.

 

It runs in the yard with no issue ran about 45 minutes the other day as soon as there is a load it acts up head scratcher.That's why I was hoping someone was having the same issue. I will be hanging the 25 on the bacj whenever I get back from our cruise.

 

If the tank is portable and isn't venting it will look sucked in and make a sucking noise as soon as you open it. Had the same issue with my yamaha 20 4 stroke a while back, swapped the tank and the problem stopped.

 

Tank vent problem. Also, have your fuel pump checked.

 

Ok Jimmy, you answered your own question brother! 3/8” fuel hose and a 16’ run is your problem. The little pump can not pull the weight of the fuel that far! Drop down to a 5/16” fuel hose and your problem will most likely be remedied! You can test the theory by putting the tank in the back with a short hose and run it before replacing all the fuel line, but I am willing to bet a sammich that this is your problem!

 

Thanks boatbrains I'll try that

 

If the bulb is sucked in after running a load, that’s because you are pulling more gas than air is entering the tank/vent. Basically a vacuum and at some point the fuel pump won’t pull any more. Everything works till it breaks. Don’t rule out tank or vent issue just because it used to work.
However I think Boatbrains knows more about boat motors than me.

 

Maybe that's what I need to try with my HB.... drop to 5/16 on all my hosing.

 

my jonboat has tank up front, with an inline filter, when i get to bout a quarter tank, i start having issues as well. check fuel level.

Also

My hobie skiff did the same thing about 5 miles off ft lauderdale, bumping around made the fuel connector from the tank to fuel line got clogged wit a tiny piece of silicone... something is clogged.

Try running a smaller line too! im running 1/4 or 5/8 in both boats.

 

Also check to see if you are "making oil" or your oil smells like fuel. I have had two Yamaha 15s of that generation come through with perforated fuel pump membranes. They would run but couldn't pull enough fuel at high throttle.

 

Yes, this too!

 

When under a load the motor is demanding more fuel and the pump is sucking harder. A lot of outboard issues don’t show themselves on the hose or at idle but when you put the hammer down they show themselves. I could see how too small a fuel hose would cause fuel delivery issues on a small outboard and a long tank run but why would the bulb go flat? My fuel hose on the 70 is 5/16” and the run is about 17’ because of high motor mounting.

 

I missed that part. I only saw the lost prime. In your case, there is one of the following:

1: collapsed or obstructed fuel line before the primer bulb.
2: faulty valve in the primer bulb.
3: faulty anti-siphon valve.
4: fouled vent.
5: fouled pick--up in tank.

 

Post a pic of the fuel line. Something is not jiving.

 

Also, is this one of the new EPA compliant tanks?

 

Here you go

 

Another possible reason...the light grey fuel line you show may have a thin clear plastic liner inside. This over time collapses and turns to sh**. Been there.

 

Brand new fuel line no inner tube had that issue also before. It did the same thing with the old fuel line also I believe it is in the motor as suggested by someone else. I have decided to put the 25 on it and pull off the 15 that will definitely fix the problem as I know the 25 will pull the gas that far. Now I just need to see if a 9 gallon tank will fit under the front deck.

 

So to be clear, is the bulb sucking flat or just losing prime?

 

Collapses but not all the way flat.

 

If the bulb is collapsing, I'm having a hard time seeing this as a motor issue.

 

Jimmy, if the bulb is collapsing/sucking flat then your problem is most definitely a restriction before the bulb. I can say this without a doubt brother! I misread your posts and thought it was losing prime.

 

I agree 100%!

 

That full line you posted most certainly does have a liner, every B1-15 line has it with the exception of Sierra Silverado 4000 and a certain Gates love. Also, B1-15 is soft in general. Go to an A1-15. If your running long runs, you need LARGER hose. It has nothing to do with the weight of the fuel, but the pressure loss caused be fluid friction within the hose. I don't see the diameter as the issue however.

 

It could be the disconnect on the tank.

 

I would agree if it hadn't happened with 2 different tanks 2 different gas lines 2 different primer bulbs and 2 different set of fittings that's the only reason I posted it I am halfway smart and I use that term losely the only constant is the motor.