Outboard fuel starves at 2700-3000 rpm-

[mfsb]

I have a wonderful boat I really enjoy that is having an interesting issue I hope someone can help me with. I have a 1985 Johnson 140hp 2 stroke engine. When I idle away from my dock it runs fine, purrrrrrrrrrrs right along. if I jam the throttle to full open, or slowly open it to full open it runs fin as well. But!!!!!, if i push it just up to 2700 ish, or even as highas 3000 ish, it will starve for fuel. Initially I thought it was the fuel bulb or vent on the fuel tank, so I have done both of the following. I have run it with the fuel cap off in the same conditions, no change. I also replaced the fuel squeeze bulb with a new one from sherwood. again, no change. I think I have a problem with anti-siphon valve possible sticking and causing it to starve for fuel???? If while it is sputtering prior to fully dying, I jam the throttle to like 3/4th or more it will continue to run and accelerate with no issues, but if I leave it the engine will eventually die. I can restart it no sweat!! I crank for just a couple of seconds and it fires up like no issue, just mid range throttle the engine starves for fuel. I have a clear, cleanable fuel filter and have watched it empty of fuel as this is occurring so I know it is a fuel delivery issue, just not positive where to look. I was thinking maybe fuel pump has an issue? but wouldn't that show during idle and all other rpm ranges as well? I suspected the anti-siphon valve because it is just a simple spring valve that works against suction right, that with little to no suction it closes preventing fuel flow, so if it is sticking partially closed then moderate demand would not be able to overcome it, where as high vacuum can push it open??? Any other ideas would be greatly appreciated!

 

[fireman57]

Re: Outboard fuel starves at 2700-3000 rpm-

If you want to check your fuel pump have someone squeeze the bulb like they were possessed and if it picks up and runs then your fuel pump is going bad. Does the engine get passed this problem and run WFO with no problem?

 

[Stuarth]

Re: Outboard fuel starves at 2700-3000 rpm-

Think I am having same problem as you mate , mines is an 87 150 vro it's doing my head in

 

[willy007]

Re: Outboard fuel starves at 2700-3000 rpm-

You might have a dirty or clogged intermediate orifice in one of your carbs... If you can punch it at full throttle and don't have any acceleration problems then I doubt that your pump is the problem, it can obviously keep up. You may be on the right track with a sticky valve but it's not as common of a problem and when you hear hoof beats you thing horses, not zebras.

 

[Stuarth]

Re: Outboard fuel starves at 2700-3000 rpm-

Could it not be that the pump can't keep up with fuel delivery , and it emptys float chambers ?

 

[fireman57]

Re: Outboard fuel starves at 2700-3000 rpm-

You can take the cover off and have someone look into each carb throat to make sure they are all getting the same amount of fuel when it does this. It will be lour so wear some ear plugs. if you see one that isn't getting the spray the other do then at least it is pinned down to that carb or two.

 

[mfsb]

Re: Outboard fuel starves at 2700-3000 rpm-

thanks for the help. I have suspected the carbs of needing some cleaning for some time and I haven't done it. I keep the boat in the water behind the house, so when I do pull it out to clean the carbs I am going to have a few things to do at once. I was thinkin maybe putting in a fuel water separator and the squeeze bulb, a full fresh tank of fuel and running it to see how it does. I am hoping it cleans it up very well and it quickly turns into a well running motor.

 

[HenryB]

Re: Outboard fuel starves at 2700-3000 rpm-

Try running on an auxiliary fuel supply to eliminate a fuel pickup problem. I had a problem with the plastic part of the pickup tube breaking partially away. Everything was fine until the boat got up on plane and the fuel level dropped below the level of the pickup tube and the engine would stall. What a bummer that was.

 

[mfsb]

Re: Outboard fuel starves at 2700-3000 rpm-

I replaced the fuel line over the weekend and for about 1 hour of running it was purrin right along. The next day, same thing ran like a champ. However night before last it was doing the same thing, hesitating and starving. This morning I replaced the anti-syphon valve and looking inside of the valve you can see a sludge build up. This sludge is clogging the valve and causing my issues. I had found this same crud in my see through filter and it has the same appearance as the varnish you find in a carb that has been allowed to sit without cleaning. It is nasty, and I would imagine all over my tank, so my question to you guys, is how do I clean the tank without replacing it. The tank is a built in model and I would guess it is all over, do I just fill the tank with fresh clean fuel and pick day I can run the boat all day and have a bunch of filters on hand? is there a process I can use that might clean this up? Or is there some chemical I can mix with the fuel that will break it down?

Bottom line, it is a bad fuel issue I am dealing with, not mechanical. The engine is a 2 stroke johnson, I am using TCW3 oil, and regular pump fuel, the inexpensive stuff.

 

[fireman57]

Re: Outboard fuel starves at 2700-3000 rpm-

I would siphon out all that I could and then put some B12 or seafoam in it and let it sit for a couple days trying to make it move and break loose. After that all you can do is put 2-3 gallons of fuel in it and siphon it again until you can get all you can out of it.

 

[mfsb]

Re: Outboard fuel starves at 2700-3000 rpm-

What do you think of pooring a whole gallon of b12 with 3 gallons of fuel and running that through with an electric fuel pump recirculating the mixture through a filter?

 

[HenryB]

Re: Outboard fuel starves at 2700-3000 rpm-

This, is what I would suggest,

How much gas was in the tank when put into storage? Not much then the sides of the tank should be free of gunk. The gunk at the bottom should clear away with use.

Do you have a water separator filter? If not, you should have. Use ethanol gas.

A water separator filter should last quite a while. Replace the inline filter at each water separator filter change.

Put the recommended amount of Seafoam in the gas.

Remove the check valve at the pickup tube.

Run the engine as normal with a spare set of filters handy.

Replace the check valve if you wish when the gunk has been washed away.