fuel flow

[rvan]

Hi all,
96 2520dvsc, BB i/o
Loss of power last week and just able to get back at low rpm/speed. Figured fuel starvation and replaced the racor, but there was still some restriction. While replacing the anti-siphon (was bad), noticed a second tank output, right next to the first, blocked off/unused.
While the anti-siphon makes sense (and is required), it looks like it would create some restriction even when working porperly; the fuel still has to flow around that ball-bearing...all inside a 3/8 tube!
Since my racor has dual inputs (and a single output), wouldn't it make sense to run fuel from BOTH tank outputs (2 anti-siphons) to the racor? It would seem that this would only enable more flow to maximise the 3/8 line at wot?
How do the guys w/high fuel flow needs get enough through that dinky anit-siphon?
Any thoughts?
Thanks,
rvan

 

[DaleH]

FWIW larger engines are pulling adequate fuel thru a 3/8" sized anti-siphon valve and as is, most motors were designed to pull thru them.

Whereads you're running an I/O boat, you need the anti-siphon valve installed. Therefore, I bet you also has a screen installed on the end of your fuel pick-up screen. Remove the pick-up by removing the fuel line and unscrewing the fitting on top of the tank, using 2 wrenches.

I bet there could be "naval lint" built up on the end of the screen. Even though I run an OB, I do use an A-S valve on the tank and a screen on my pick-up ... these are checked every other season, only takes seconds to do.

 

[rvan]

Hi Dale,
Thanks for the reply!
I did remove the screen at the bottom of the pick-up. It was clean, but could be that scale or something clogs it under draw and drops off w/o load. When I pulled the pick-up I also took about 20 gal out of the bottom of the tank to check for water/sediment. Just a tad of both, but over a few hundred gallons it adds up!
What do you think about using both of the tank fittings to the racor? Is there a disadvantage? If a anti-siphon were to fail then, I'd still be able to draw from the other.
One more thing, is the yellow teflon (gas) tape a good choice for the fittings?
Thx,
Robert

 

[DaleH]

What do you think about using both of the tank fittings to the racor? Is there a disadvantage? If a anti-siphon were to fail then, I'd still be able to draw from the other.

Boy if anything, my first inclination is that if you did this you just added yet another fuel restriction into the equation for the load on the fuel draw ... so with that, I'd have to say "no way", but it's just my opinion, as I'm not an authority on fuel pump draw.

One more thing, is the yellow teflon (gas) tape a good choice for the fittings?

I used to use tefon tape and never had a problem, but have read stories where it can "creep" up the threads, so I now just use Permatex #2A, which is a fuel-rated non-hardening sealer.

I think you need to get back to the root cause of your performance issues and it sounds like you cleared the tank and AS valve as being the culptit. What is the rest of your fuel line made from? Is it tubing or A1 rated hose?

I have heard of some hose-type lines breaking down to where it caused fuel delivery problems ... but my Dad had a small leak on a metal (copper?) fuel line where it wouldn't leak fuel, but under vacuum/load, it would leak air and that caused his RPMs @ speed to suffer.

 

[rvan]

Hi Dale,
Thanks again for the input.
I decided to run the two new lines from the tank, but put a small fuel shut-off valve where each meets the racor inputs (eng compartment). I'll leave one normally off, but can then easily switch inputs if one fails. I used the Permatex 2a instead of tape as well. BTW, good link on this forum for the 3/8NPT anti-siphon. All I could find elsewhere was 1/4.
I have a large 4 scoop sitting above the tank deck plate, so repairs there at sea are difficult.
Playing it safe.
That should end flow problems upstream of the racor! Downstream is easily accessable.
Regards,
Robert