Primer bulbs

eeshaw

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What's the rule of thumb to use a primer bulb in a fuel system?
 

Stove Iron

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They have always worked fine for me. When I prime my Yamaha built Mariner, it fills the external fuel filter assembly and pushes fuel through the fuel lines to the fuel pump. Thereby "priming" the fuel system.
 

cyclops2

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Mine works fine horizontally. That allows it to always be full of gas all the time. It is at the lowest point of a 16' fuel line run and holds a prime all winter. BUUUTT Only use Marine High Test gasoline from a commercial workboat fueling dock. NEVER have had a bad load of gasoline in 40 ?? years.
 

eeshaw

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Does engine size make a difference? Do larger engines require one in the line from the water seperator to the engine?
 

cyclops2

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Engine size DETERMINES squeeze bulb size & the I D inside diameter of the USCG Approved fuel line from fuel tank to engine connector. You must be SURE of all the sizes & parts to be used.

Your life can & does depend on all parts of your boat working everytime.
DO NOT buy the cheapest parts. Unless you can walk & swim with alligators & Boa Constrictors. They kill & eat people walking their dead boat around.
 

Tin Man

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With OB fuel line assemblies that include a primer bulb....I prefer OEM by manufacturer of OB. They tend to be of higher quality overall. My last OB had a Honda OEM fuel line with bulb that lasted 20+ years with no leaks. Granted, current materials/craftmanship aren't what they were 20-30 years ago, however, my recently purchased Yamaha assembly appears to be of very high quality (Made in Japan).
 

Pappy

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A primer bulb does not stop at the fuel pump. It takes the place of the fuel pump and will prime a system all the way to the fuel bowl until the needle and seat closes or will fill a vapor separator tank on an injected engine.
 

cyclops2

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I have run carbed engines with just squeezing the bulb. 3 of us took turns to make it back to the dock
 

MrGiggles

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Does engine size make a difference? Do larger engines require one in the line from the water seperator to the engine?

Engine size may require a 3/8 hose rather than 5/16 which is most common. 115hp is roughly the cutoff there.

Many EFI engines do not recommend use of a primer, as it can flood the VST. Not all of them have floats and needle valves, but instead rely on an electrical switch to cycle the lift pump and maintain the proper fuel level.
 

eeshaw

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The reason I asked the question is the boat I'm working on is a 20 foot Mako. I'm putting a 125 Mercury 2 stroke on it. The fuel line runs from the tank to a water seperator in the bilge, but from the seperator to the engine there is nothing. If it requires a primer setup then I'll put one in. I've only dealt with smaller outboards is why I asked.
 

airshot

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On my Islander, the fuel tank was moved farther forward by more then 6', really helped the boat to trim out much easier !! That long fuel run would take a long time to prime if the boat sat for weeks. I added a primer bulb to speed up the process. Instead of cranking for 5 minutes or more a few squeezes and the engine would start right up. I replaced mine with a cheap Wally World brand and it sprung a leak in less than two years....not a place to go cheap !!! If you add one buy a good brand name bulb !!
 

Pappy

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The reason I asked the question is the boat I'm working on is a 20 foot Mako. I'm putting a 125 Mercury 2 stroke on it. The fuel line runs from the tank to a water seperator in the bilge, but from the seperator to the engine there is nothing. If it requires a primer setup then I'll put one in. I've only dealt with smaller outboards is why I asked.
Thought you would have picked up on the answer by now but......the answer is YES, you need a primer. Unless you want to absolutely wear out your starter trying to lift fuel to the carbs with a pump that only works while the crankshaft is turning and producing a vacuum/pressure pulse
 

eeshaw

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I picked up on the answer, I just wanted a sanity check. I've seen pontoons with 90's and 115's that have nothing, for that matter I've never seen a bulb on any of those. Maybe that's because the engine sits below the fuel tank? Anyhow, thanks for all the information folks, it's much appreciated!
 
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Pappy

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Realistically I have probably rigged well over 500 pontoons (that number is conservative) in the last several years. Every single one goes out with a new primer bulb on it. Period.
 

FuzzyGrub

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FWIW: Our 2022 G3 w/90hp power head came with water filter and primer bulb. Yamaha EFI four stroke jet.
 

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