Losing fuel "prime"

[Lezm001]

I have a 115 HP Johnson faststrike motor (J115GLEDR) that has a problem related to what I'm calling fuel pressure. I always need to pump the primer bulb several times before starting. The motor starts without any problem. Motor runs fine while driving the boat. The problem occurs after I've been fishing for awhile without the motor running. Let's say 45 minutes - 60 minutes. I'll need to give the primer bulb a few more pumps before starting the motor. I've replaced the primer bulb twice with an OMC primer bulb and that doesn't solve the problem. I'm starting to wonder if this may mean that the fuel pump needs to be rebuilt?

This is my thought process, please correct any errors.

Fuel line from gas tank to primer bulb and primer bulb to engine appears fine. No signs of fuel leaking. Since I need to pump the primer bulb, the fuel in the line must be going somewhere. I don't believe it is flowing back toward the fuel tank, the fuel would need to flow "up hill". If the fuel in the fuel line is draining toward the engine, would this mean it is getting past the fuel pump? If all seals / diagrams are ok in the fuel pump would this prevent fuel from "flowing" to the carburetors?

Appreciate any thoughts anyone has on this.

[tdt91]

Maybe this has warped? The pros will come along soon enough.

Johnson 0433000 - *FLOAT CHAMBER Assy | Boats.net

[Bighare2]

True to float chamber issues as possible. But more Questions first. Why do you expect the fuel system to remain under pressure between the primer bulb / fuel tank and the fuel pump? On a carbureted engine the fuel system is not intended to remain pressurized once the engine is turned off. Fuel pressure relaxes as between the pump and the tank as soon as the engine starts to run.
please describe your general starting process when the engine is cold and when warm. How to you manipulate the key switch to engage the primer solenoid when cranking the engine? Do you hold the key pressed in or do you release it?

[Lezm001]

When the engine is cold, I pump the key 2 times and keep it held in while starting the engine.

When warm, if I haven't been fishing long (maybe 30 minutes or less), i can usually restart the engine just by turning the key.

When I've been fishing longer and need to pump the primer bulb a few times, I usually also need to push in the key when starting.


When you say fuel pressure relaxes, does that mean fuel should flow back toward the gas tank?

[ChampioNman]

Inspect your carb bowls for warping. If the gaskets between the bowls and carb bodies are black time to replace and rebuild the carbs and replace the float bowls if warped.

[Bighare2]

No - fuel does not flow back to the tank. There is an anti siphon valve at the fuel tank (usually) plus the check valve in the primer bulb.
Pressure relaxes when the float valves in the carbs drop. The primer bulb intent is to make sure the carburetors are full.
Your starting process with the key is correct.
So now let’s go back to tdt91 and Championman post on warped float chambers and fuel allowing fuel to vaporize.

[ChampioNman]

To add to Bighare2's post with fuel system on the 60* engines, especially in summer time, the fuel vapors "boil" in the vapor tank and you get an almost "vapor lock" condition. Pumping the primer gives the system a shot of fresh "cool" fuel to the carbs pushing old "hot" fuel out. A failing diaphragm in the vapor pump can cause this to occur also.

[Lezm001]

Thanks to all of you for the ideas / feedback. I'll take a closer look at the carburetors.

Are the vapor pump and fuel pump the same thing?

[ChampioNman]

No the Vapor pump sits on the vapor tank, it is actually a 6HP engine fuel pump. The fuel pump is the VRO/OMS pump.

[Simply_M]

If the engine is tilted up you may lose fuel from the carburetors and have to reprime.

[Lezm001]

Question about the vapor pump diaphragm, is their a way to determine it is bad other than just buying a new diaphragm and rebuilding it?

[ChampioNman]

No you can't tell.

[Lezm001]

If the carb bowls are warped, should I be able to see fuel leaking in that area when pumping the primer bulb?

[ChampioNman]

Yes you will see seepage at the gaskets or another place would be at the small BB on the bottom of the bowl.

[Lezm001]

I've looked all of the carbs over and the vapor pump area while pumping the primer bulb and don't see any leaks. I did notice that the two starboard side carbs have very dark colored gaskets between the bowl and carb. I had some work done on the engine last fall and the carb bowl gaskets on the 2 port side carbs are new.

If I replace the diaphragm on the vapor pump, is it just one diaphragm? When looking at the vapor pump, it looks like their may be two gaskets involved in the vapor pump assembly?

Another question about the carburetor bowls, since they are plastic, they are never going to be 100% flat, is the more important item to replace the gaskets? Do fresh gaskets make up for any "warp" conditions?

[ChampioNman]

As you can see from the contents of the carb repair kit (this is an OEM kit) the gasket between the carb body and float bowl is tan/brown. The gaskets are ethanol resistant. Another thing on the warping there is a small gasket that seals the emulsion tube in the center of the carb bowl this can cause the loss of prime. New bowls will be flat. There is a raised lip on the edge of the bowls that helps seal the bowl to the gasket and carb body.

[Les Young]

I just had all 6 carbs rebuilt on my 2003 johnson 175 & it was worth every penny of it. It ran good anyway but has never ran as good as it does now.

[Lezm001]

Great feedback from all, thanks so much. I will be ordering carb rebuild kits and new bowls. I do have a question about the ball bearing covering a hole on the side of the bowl. I've seen youtube videos saying that you'll eventually develop a leak in that area and that you should epoxy / JB weld that hole shut. I'd appreciate your thoughts on this? I'm assuming the hole and ball bearing has a purpose.

[ChampioNman]

Very rare for that to happen but I use marine tex when that happens epoxy doesn't do well when it encounters fuel. Don't need much.

[Lezm001]

If I replace the diaphragm on the vapor pump, is it just one diaphragm? When looking at the vapor pump, it looks like their may be two gaskets involved in the vapor pump assembly? Possibly also an O-ring. Appreciate thoughts on what parts to order if I remove the vapor pump to replace the diagram