2006 90hp with a portable tank. The manual says to use a 5/16" fuel line for 25hp-130hp. My boat has a 3/8" fuel line for some reason - I guess they made a mistake when they installed the engine. I have owned it for 2 years and it has run flawlessly. I came across the fuel line problem this week while troubleshooting a warm starting problem. Cold starts and runs perfectly
but after an hour of sitting it take 10+ key turns to start. Someone suggested I stop pumping the ball (and choking) before starting it after the hour. I don't think the fuel line size is related to the issue but I wanted to know the forums opinion of the suggested 5/16" vs. the 3/8" I have been using. JoinedSep 24, 2008Messages8,958
Re: Fuel Line 3/8" vs. 5/16" I would stick with the 3/8 fuel line. JoinedDec 9, 2005Messages11,551
Re: Fuel Line 3/8" vs. 5/16" The size of the fuel line is unrelated to any problem. Your engine will run fine on either 5/16 or 3/8 line. If you had a V6, the 3/8 line would be required. Unlikely you should need to reprime the fuel hose bulb during the same day of operation. You may only need to re-choke the engine when it cools off, usually after a few hours.Daviet
Fleet Admiralemdsapmgr
Supreme Mariner
Last edited: Sep 8, 2010
- #4
Re: Fuel Line 3/8" vs. 5/16" Two votes for keeping the 3/8" is good enough for me. How about pumping the ball until stiff on an engine that has been running for awhile then sits for an hour? From what I understand it shouldn't matter if I pump it again since the carb floats will keep out the gas.
- #5
Re: Fuel Line 3/8" vs. 5/16" just read your response about the ball pumping. thanks - I think I will lay off the choking and pumping on the restart after the hour long sit. Hoping this will solve the problem.
JoinedJul 30, 2006Messages3,740Rick.
Captain
- #6
Re: Fuel Line 3/8" vs. 5/16" I can't see a reason why it would hurt anything. On the other hand it is probably not necessary after just one hour. I think it is one of those things that you have to learn what is best for your motor. I don't pump my bulb (85-40 HP. Johnson) at all during the day after the initial cold start and that works well for me. My little motors (15 and
under) do seem to require a bulb pumping after sitting for a while during the day but don't normally require choke after the initial cold start. I too agree there is nothing wrong with 3/8 fuel lines even if 5/16ths. is good enough. Rick.
JoinedJul 22, 2010Messages13Seth2904
Cadet
- #7
Re: Fuel Line 3/8" vs. 5/16" i would have to agree witht he fuel line i would stick with the 3/8's line it sounds like it has to do with the carbs
Originally posted by david123 View Post
I am not sure. Existing installation has a: 5/16 (8mn) line from tank to water separator filter, and a 3/16 line to the outboard. Should the lines have tge same diameter?
Is 3/16" , ^^^, a typo (I hope)?
If the tank to fuel filter is 5/16th's, you can keep it the same...
Make sure you get MARINE RATED FUEL LINE.
It does make a difference with ethanol breaking down the innards of some regular fuel line...
03-16-2004, 05:34 PM | ||||
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Again, I don't have my reference book with me, so somebody correct my math if it's wrong here. I'm trusting the formulas given above for these numbers. A motor with a specific fuel consumption of .50 lb/hr/hp, producing 500HP, does indeed need 250 pounds per hour. But gasoline is more like 8 pounds per gallon. 250 pounds per hour equals 31.25 gallons per hour. 1 hr =3600 sec 13 sec = .0036 hr. 31.25 gallons per hour times .0036 hr equals .113 gallons needed for a 13 second run. That's a little less than a pint of gasoline needed for the run. There's a LOT of energy in this fuel we burn! Using the formulas given above, a 10 ft fuel line, 5/16" dia with a .035 wall thickness will have a volume of about 22 cubic inches. A 10 ft fuel line, 3/8" in dia with a .035 wall thickness will have a volume of about 35 cubic inches. If one cubic foot (1728 cubic inches) equals 7.48 gallons, then one gallon equals 231 cubic inches. One-eighth of a gallon (the one pint used for the run) equals, oh, let's round it off to 30 cubic inches. That means there's a little over one pound of fuel in the 3/16" line, and about three-quarters of a pound of fuel in a 5/16" line. So, when we go through the lights, the fuel that was at the back end of the 3/16" line is just getting to the carb. If we have the smaller line, we'll burn all the fuel that was in the line, plus about 25% or so more. Seems to me that the more critical specification of a fuel pump is its ability to maintain the correct pressure at launch, not necessarily a huge volume, although it would be hard to achieve one without the other. |