Gas line size

Joker2 · #1 06-15-2012, 04:35 PM

Hey guys i had a thought about my RPM problem, ( only getting 4500 ) I have been through all the checks in the past 1-1/2 years, when I did my new transom ( 2 Yrs. ago ) I replaced all fuel lines and added a water seperator, I used 5/16 lines, someone mentioned to me they really should be 3/8 ! could this be why I am not getting full RPM's ? Thanks

phatdaddy · #2 06-15-2012, 06:50 PM

run it off of a seperate 6 gallon tank w 3/8 hose and see if problem goes away.

tsubaki · #3 06-15-2012, 08:12 PM

I'd do like phat said!
I can't remember the usual breakdown as to hose size per cylinders used.
Seemed like it was 3 cylinders can run off of 5/16 and 4 cylinders might be able to but the 6 cylinders need 3/8.
I'm sure you will find a smaller line size at or in the engine than what comes from the tank, if you try to rationalize it that way. Figure trying to suck through a small straw and the volume you get compared to a McD's straw.
Adding more hose length and another filter should compound the problem if the hose size was borderline.

THEFERMANATOR · #4 06-15-2012, 09:22 PM

5/16" line is margianal, but if your engine is wired properly you should have an alrm go if for excess fuel restriction. It would go off it the smaller line was a problem. It won't hurt to go up to 3/8" line. If the line was your problem though, it would rev up and then die down as it ran out of fuel, it wouldn't be that way all the time. 3/8" line flow alot of fuel. I know I set-up a buddies boat with dual 100 gallon tanks and a pair of 225 EVINRUDES on the back, and put in a 3 valve manifold set-up in the back. I could go full power on BOTH engines pulling through 1 fuel seperator and the single 3/8" line. It was marine grade line though, so it doesn't collapse like the cheaper auto grade line will under vacuum. So if I could run 450HP off of 1 3/8" line, I would venture to say that a 5/16" line would probably feed 150 HP.