Running out of fuel when wide open

[Motox125]

Hi all.   I took my 1998 175 out to lake test the internal tank rebuild this week and it runs well and long at lower RPMs but cuts out and dies after being 1/2 to full throttle for 20 seconds or so.  The primer bulb is empty after this happens.  I'm able to re-prime, restart and repeat the failure mode. 
I brought along the external tank and it worked fine at full throttle forever.  This bypasses the anti-siphon valve and water separator.
More about the internal tank rebuild..  When I bought the boat the fuel sending unit was gone and the taps for it were dissolved.  In the process of fixing that, the internal tank was cleaned out and the fuel pickup tube and fittings were replaced.   Care was taken to make sure the pickup tube was cut at a slight angle and at the correct length when the fitting was fully screwed in.  Permetex 3 was used on everything and a pressure test with soapy water was performed to ensure goodness.   I chose to go with a fuel pickup fitting/barb with the Moeller anti-siphon valve.  A new fuel/water separator filter and flush mount fuel vent were installed as well. 
After putting about 10 gallons in the tank I used the primer bulb to fill everything and then ran it in the yard for about 10 minutes prior to the lake test. 
I do notice that when priming to the point of the bulb being hard, a few drips of gas come out where the fuel line connects to the motor (1999 Merc 115 ELPTO) -  but I don't think this is causing the issue. 
I'm planning to replace the anti-siphon valve with a straight thru fitting barb and then retest.   
The reasoning behind this is that I read a few articles stating they could cause issues. 
This will likely be a pain since there is not enough fuel line to cut it and I know the barb connection is super tight.. So, before I try that I'm wondering if anyone agrees with this approach.   It is possible that the fuel pump can't pull enough fuel through the anti siphon check valve under high demand? 
Any other possibilities?
Thanks in advance!

[Flapilot]

Had this happen on my old boat and it was the anti siphon valve.

You may also want to check the vent line.  If possible without getting water in the tank, Run the boat with the fuel cap open and see if it changes.  If it runs fine with the fuel cap open it may be the vent line.

[boatnamesue]

I think I read somewhere that having an anti-siphon valve is required, yet I definitely read that it gives boaters major headache.  And it sounds like it's your issue. 

Although the fuel leak engine side isn't the cause for the primer bulb collapsing, it's definitely cause for attention.  Don't want fuel leaking from anywhere. 

[CTsalt12]

Hi all.   I took my 1998 175 out to lake test the internal tank rebuild this week and it runs well and long at lower RPMs but cuts out and dies after being 1/2 to full throttle for 20 seconds or so.  The primer bulb is empty after this happens.  I'm able to re-prime, restart and repeat the failure mode. 
I brought along the external tank and it worked fine at full throttle forever.  This bypasses the anti-siphon valve and water separator.
More about the internal tank rebuild..  When I bought the boat the fuel sending unit was gone and the taps for it were dissolved.  In the process of fixing that, the internal tank was cleaned out and the fuel pickup tube and fittings were replaced.   Care was taken to make sure the pickup tube was cut at a slight angle and at the correct length when the fitting was fully screwed in.  Permetex 3 was used on everything and a pressure test with soapy water was performed to ensure goodness.   I chose to go with a fuel pickup fitting/barb with the Moeller anti-siphon valve.  A new fuel/water separator filter and flush mount fuel vent were installed as well. 
After putting about 10 gallons in the tank I used the primer bulb to fill everything and then ran it in the yard for about 10 minutes prior to the lake test. 
I do notice that when priming to the point of the bulb being hard, a few drips of gas come out where the fuel line connects to the motor (1999 Merc 115 ELPTO) -  but I don't think this is causing the issue. 
I'm planning to replace the anti-siphon valve with a straight thru fitting barb and then retest.   
The reasoning behind this is that I read a few articles stating they could cause issues. 
This will likely be a pain since there is not enough fuel line to cut it and I know the barb connection is super tight.. So, before I try that I'm wondering if anyone agrees with this approach.   It is possible that the fuel pump can't pull enough fuel through the anti siphon check valve under high demand? 
Any other possibilities?
Thanks in advance!

I have the same boat and basically same engine, and have this issue a few different times for different reasons.  What kind of tank is it?  Poly, aluminum?  Fuel pickup could definitely be it.  Definitely check the vent by running wide open with gas tank open as someone else mentioned.  It could also be a blocked screen at your fuel pickup in the tank.  When you cut the pickup tube, did you install a screen?  Beyond that, I would check all lines from the tank to the engine.  I have a line from pickup to water separating filter, than a line from filter to the primer bulb.  Then of course the primer bulb itself, but assuming you use the same one for your remote tank and your fixed tank, that shouldn't be the issue.  Take them off, visually inspect, and blow some air through it.  Lines deteriorate eventually, some others with more experience can share the average time for them to deteriorate.
 Should be easy enough to diagnose. 

I would also check your fuel water separator while you're at it.  My guess is that during your tank fixing process, some debris got in your lines or pickup.  My pickup I can 'pop' out of the tank, it's only affixed with a rubber o-ring.  That's an easy one to check.

[Motox125]

Thank you all for the replies.
Took the boat out tonight and it ran great!
Changed 2 things. 
1.  Removed anti siphon valve.
2.  Swapped out the $4.88 Walmart Attwood fuel connector (for Mercs) with a new one.   Still leaked when primed up.  Then changed to the one that was on the external tank (couldn't find and logo on it but it slightly different)  and it audibly clicked in.  Prime like crazy and no leaks. 
One wonders if the fuel leak was enough to lose just enough suction to not fully open the anti-siphon-valve. 
To answer the other questions, the internal tank is poly. 
I did not install a screen on the new fuel pickup tube..  Should I have?
New fuel vent.  Tested good by blowing compressed air into the tank.
Brandy new fuel separator.
Thanks again. 
Just in time.  The big girls are in town!