I'm installing a whippled 496 HO in a 94 Eliminator and I'm redoing all of the fuel plumbing. Currently there is a 90 degree brass fitting coming out of each tank, screwed into that is a barbed brass fitting that contains the check ball. The opening containing the check ball is only about 1/4" and I'm concerned about about fuel flow restriction (thats why I'm replacing all of the lines and the valve). So the question is can I just eliminate this fitting and run my fuel lines from my switching valve directly to the brass 90 coming out of the tank or will I be screwing things up? I don't really understand the purpose or function of the antisiphon device, any input would be greatly appreciated.

Get rid of the restrictive checkball assembly. You should upsize ALL fuel lines including fuel tank pickup to 1/2 inch minimum. And don't overlook your fuel tank vents either.

Antisiphon device: keeps fuel from siphoning itself into your bilge.

Picture this: your saddle tanks are mounted up pretty high. Your fuel line runs all the way down to the stringer mounted water separator. Then to the mechanical fuel pump and on up to the carb.

If your spin-on separator got loose, or your old fuel line got a crack in it, or the wrench monkey from the marina that you let winterize your boat stepped on the fuel line and pulled it halfway out of the fitting, then without the anti-siphon checkball, your entire contents of the tanks would end up in the bilge.

This is not as MUCH of a problem with a center keel tank, but if the belly tank is full, you can still siphon it all out. Especially when underway (nose-up).

If you remove the checkball, and EVER have a gasoline related insurance claim, you WILL be denied.

My advice is to buy a larger antisiphon assy that will flow the required volume of fuel.

I second what mcollinstn said , particularly the insurance part.
Also to aid fuel flow avoid drilled or cast 90*s after the fuel pump. Bent or formed 90*s are better. When you suck thru a 90 , the fuel tends to go in the directon of the suction. But when you are pushing the fuel and it hits a drilled or cast 90 it tends to back up and restrict flow due to the fact it just wants to go straight while being pushed. If you use a formed 90 , it helps redirect the flow around the bend and keeps it flowing

Thanks for the replys. Any ideas where I can look for larger anti siphon devices. I don't know that I've ever seen them anywhere.

Correct me if I'm wrong but isn't the checkball to prevent fuel from siphoning back to the fuel tank? This helps prevent extended cranking times after sitting. I have never seen a larger check valve for a blower application. You guys have enough paranoia for a crowd.

i made the mistake of taking them out (duel tanks)for the same reason a 700hp merlin that needed a lot of fuel. and i put in 1/2 brass n.p.t fittings and the next morning my edlebrock 130gph mechanical fuel pump was leaking gas from all around the diaphram real bad had about 5 gallons of gas in the bilge.my boat even had a mechanical fuel valve and even with it turned of it couldnt hold back all the fuel presure.i switched back to the check valves and it stoped leaking and the fuel on/off valve was able to shut off the fuel again also.i think with all the fuel being gravity fed with 90 gallons of fuel in the tank pushing was just to much pressure to hold back.i talked to imco i think they said they have a check valve with a 3/8 line which would be better than what you have at least.

You want to keep the check valve, but the problem is that it's highly restrictive and I don't know of any improved versions. It's a lose-lose situation.

HP,

consider yourself corrected.

The anti-siphon device is a USCG REQUIRED safety device. It's primary purpose is to use spring resistance to seat the ball and prevent fuel from coming OUT of the tank unless mechanical suction from a fuel pump overcomes the spring pressure.

The fact that it also functions as a one-way valve that keeps fuel from being added into the tank from that same line is a tremendously secondary benefit. Typically, the one-way valves in a fuel pump will dam up the fuel from returning back downstream without the aid of the tank's siphon device...

I've rarely been labelled as paranoid, and am usually branded an idiot for ignoring safety issues that most folks consider to be significant. Having battled gaoline fires in three boats, though, gives me a pinch of perspective into the issue.

Nimrod? Lard@ss? Bastage?
yes to all of the above.

Paranoid?
Not hardly.

OK fair enough on the valve function. Any boat I have seen or owned would have braided lines throughout and it is a much bigger concern to have inadequate fuel volume. You have had 2 fires? Are you a firefighter? j/k! Seriously though, I have had 2 insurance claims since 1988 (not related to fire) and boats were never scrutinized to find a way not to cover the claim.