carb's won't stay primed

[jrbohannon]

i have a 1984 ranger bass boat with a built-in gas tank that i just restored. i removed the gas tank and cleaned it. i replaced fuel lines, bubble and filter. i rebuilt fuel pump and carbs. now it is hard to get the fuel to the carbs and when i do it runs great but after i turn it off and it sets for awhile it loses pressure. can anyone help. thanks

 

[jrbohannon]

Re: carb's won't stay primed

the engine is a 1984 115hp merc. o/b in-line 6 cyl

 

[ondarvr]

Re: carb's won't stay primed

The check valve in the squeeze bulb is about the only line of defence to keep fuel from draining back into the tank, but air does need to be getting into the fuel line for it to drain.

 

[jrbohannon]

Re: carb's won't stay primed

thanks i will try a new bulb but i have already put 2 new ones on

 

[canoemang]

Re: carb's won't stay primed

How long do you let it sit?

I have the same motor and after a hour or so i have to pump the bulb.. not a lot but it needs it..

Its been that way with my 84,85 and 86..

Do you trim the motor up past level when your sitting?

 

[CharlieB]

Re: carb's won't stay primed

Many will not use an aftermarket primer bulb as most only have one check valve where factory bulbs have check valves on both inlet and outlet.

A second part many prefer factory is the quick disconnect fuel fittings, aftermarket O-rings have a high failure rate once the fuel pump sucks on them, allowing air to suck into the system. Factory O-rings are much higher quality.

 

[Fishcake42]

Re: carb's won't stay primed

Not meaning to tread on toes her, just asking, when you say hard to pull through what do you mean, the primer is "hard", primer is slow to re-inflate, or it feels like you are pumping air more than fuel?

Also assuming you are holding primer arrow up? If it runs once primed, check the obvious I've had no real problems with after market primer bulbs.

 

[CharlieB]

Re: carb's won't stay primed

I have seen zip ties used to hold wire harness cables and fuel hose all in a neat bundle, except the zip ties were pulled a little too tight, squeezing the fuel hose and restricting fuel flow.

 

[Fishcake42]

Re: carb's won't stay primed

I do not profess to be an expert, however I am not a fan of diagnostics by replacement and was taught at college to diagnose by halves (pick a point half way along a system and see if you get what you are supposed to. If you are the problem is later, if not the problem is before. Then repeat.). In the case of primer bulbs - The most common piece of advice I have seen across the net for almost any running problem with an outboard seems to start with "change the bulb for an OEM". And yet, based on weeks of trawling for problems I had, I almost never came across an thread that said "thanks that fixed the problem". I am not saying they don't fail, they do, I am not saying OEM bulbs are not better, they are, however they are not as common a culprit as people think. If its brand new, I doubt its an issue

If primer bulb is very "hard" probably blockage/stuck float needle after bulb. If primer is slow to re-inflate probably air vent blocked/closed. If it feels like you are pumping air or not moving much fuel either incorrect orientation or air is getting in to the line before the bulb (possibly blown check valve in the bulb but unlikely if its new).

M

 

[CharlieB]

Re: carb's won't stay primed

Two simple test may help determine which way to go.

First, disconnect the fuel hose to the carbs, point it into a suitable container, pump the primer until you get fuel, then crank the motor and observe the fuel stream. You should see a nice strong pulsed flow, any less is either a restricted hose, fitting, or poor sealing valve in the fuel pump.

Second, replace that section of hose with a clear hose, run the motor and watch for air bubbles passing thru indicating air sucking in at some point before the fuel pump.

REMEMBER, remove that clear hose once finished as it is NOT rated for fuel use, only for short term testing.

 

[Silvertip]

Re: carb's won't stay primed

And a couple more tidbits to chew on. When you initially squeeze the primer bulb you are forcing fuel into each carburetor float bowl until the float and needle & seat shut off the flow. When all are full the primer bulb should be firm. Now then -- the moment you start the engine fuel is being "drawn" through the line from the tank so the primer bulb no longer stays firm because the system is no longer pressurized. It doesn't need to be since the fuel pump forces fuel to the engine after being sucked from the tank. Also, since the fuel enters the top of the float bowl, it cannot drain back to the tank. So the long and short of this is that if the engine is hard to start after shutting it off, there is: 1) a starting procedure problem, 2) carburetor problem, 3) a primer/choke system problem.

 

[Texasmark]

Re: carb's won't stay primed

My engine is a 3 cyl with a built in, always vented tank. I recently had all 3 carbs off. My engine sits for a month or so at a time. The fuel drains back over that period. I like that because it allows my needle valve to unseat and prevents a grove from forming. I have a recent new Quicksilver squeeze bulb and a new fuel hose and fuel pump kit installed. Engine always did that.

I had a 115 tower years ago. It's a long way up to that top carb. Side note: I used to run it at 6000 rpm at WOT and after I ran for a few minutes the engine would loose power. Top carb was running out of fuel. I rerouted and shortened my fuel line and solved the problem.

On fuel getting back into the tank, it's called siphoning. Since you have a solid line of fuel from the squeeze bulb up to the carbs and static pressure of 1/2 psi per foot and with the venturi tube (open to the atmosphere) sticking in the carb bowl, you have the perfect setup for siphoning.

On the trouble shooting technique Fishcake mentioned, we called it "Divide and Conquer". Can hurt you if you are leading your army and make the wrong decision, but works for trouble shooting as does answering the question is it fuel or spark.

Mark

 

[mr 88]

Re: carb's won't stay primed

As far as the primer bulb going bad,I got tired of replacing them. Went on Ebay and bought some 3/8 one way check valves,designed for fuel and installed them with the almost brand new west marine bad bulb,problem solved.I went back there with my new backup,which also bled after checking it with my mouth and got my money back.At 6 bucks a pop,including shipping,much cheaper and way more reliable.