Fuel problem, please help.

[nymack66]

Ok I will give it a shot,
Run it with an external portable tank to eliminate the possibility a vapour lock (clog air vent or bad fuel cap) or anti syphoning valve issue on the tank.
If problem persist you will need to do a fuel pump test, I am not sure what the procedure will be on a YamahaEvinrudeJohnson :)

[whatknot]

I'm going with the fuel pump doing a slow death on you. I think your supposed to have 45 lbs pressure on the bar. Mine crapped out recently and I was pushing 5 lbs. That's only a guess....Good luck with your real mechanic!

[willy]

Blue from my previous experience with a similar problem, make sure your primer bulb is good, I went thru three before I found a good one believe it or not. Second time with same problem, in engine filter was clogged and the fuel pumps had taken a dump.
That was inspite of a Racor 10 micron set up.
The Mercury did the same thing on me but it was a fuel line that had a small split in it and would take on air, same thing when I pumped the ball it did OK cause I was forcing fuel into the engine but let on its own the darn thing would suck air.

[HookedOnMarsh]

I'll bite I guess. You mentioned that the primer bulb was going flat. If you're not mashing it and it's going flat on it's own then you just ruled out your engine and fuel system from the bulb to the engine. Period. Has to be.
The problem lies between the other side of the bulb and the fuel in the tank. Maybe something is clogging up the inlet strainer in the tank? Bad primer bulb check valve(happens to me every 2 years). Trash caught in the shutoff valve at the tank, collapsing hose between the bulb and the tank. Or most unlikely, but not forgotten is a clog in the air vent.
Hope this helps.

[THEFERMANATOR]

Is the racor before or after the racor? If it is before I would replace it. I change my spin ons pretty regularly espescially with this ethanol crap we get now. Also what fuel line are you running? Make sure it is a new style marine grade line as most automotive lines are not meant to run under a vacuum like an outboard does. Verify the tank vent is good. I pulled the one out of my pro line even though it looked new and it had a big chunk of corrosion inside it. It still flowed air, but not enough when I dropped the hammer. Also if your tank has a anti-drainback valve in it, pull it out and clean it. Over the years that check ball gets varnished pretty badly and will cause it to obstruct the fuel pick-up. Most people just remove the check ball from them to prevent from having this problem. Start with basics and go from there. Also I like to use marine grade EFI fuel line as it is HEAVY walled and will not collapse even when you are hammering down on it.

[JohnnyO1]

Blue Runner

I kind of had the some problem last year. Know matter what I replaced my primer ball kept on collapsing. It usually would happen anytime after 3000 rpm. I pretty much replaced everything before the motor and now motor runs perfect.

A couple of things that I learned during the process:

1. Just because you have a brand new primer ball it doesn't mean it is working properly. I replaced my primer ball with one made by tempo later to find out they had a problem with them. Went with one made by Quicksilver for Mercury and no problems since.

2. There is something called a anti-siphon valve in your fuel line. Basicly it is a fitting with a spring loaded ball that prevents fuel to return to the tank. If the ball is frozen it could cause a restriction. Usually located after or at the fuel pick up by the tank.

3. The new ethanol fuel has a tendancy to degrade older fuel lines. That being said a piece of the fuel line could have broken loose and caused a restriction. If you replace your fuel lines just remember there are two types. One that can be exposed to uv light and one that cannot.

4. The fuel pick up has a screen in the tube. With the new ethanol fuel removing any dirt in your tank it is possible that dirt could be clogging the screen in the pick up tube. I spoke with a Mercury Rep. at a boat show and he told me to remove the screen as long as I have a fuel filter. Upon removing the screen I noticed some dirt built up on the screen which could have restricted the fuel.

5. I also changed my fuel filter to a racor fuel filter/water seperator. I did this because everything else was replaced. Filter has a clear plastic bowl which is easy to see water building up. I drain it about once a week.

That being said I have a Mercury motor not a Yamaha but I would think that the fuel delivery would be similar.

Hope this helps.

Good Luck!

[Cam]

ALL excellent advice!!!

[Blue_Runner]

Thanks fellas!

I hauled it down to High Rock yesterday evening to run it on a separate tank. It behaved the same except the primer ball stayed firmer but still felt as if it had air in it. Best I could tell anyway - it was just me so I had to pull it down to check the ball.

A couple things -

* tank vent is clear. I can blow into the tank.
* fuel tank pickup seems clear - I'm able to blow bubbles in the tank.
* I'm running a racor /w the clear bowl. The racor is before the primer.
* when running on spare tank I bypassed the racor.
* I would love to replace fuel lines, clean the pickup screen, etc. but will have to remove the tank hatch to access it. It has never been removed.

I think I have ruled out - primer bulb, fuel lines (unless it is the short piece from primer to motor which is only 5 yrs old), fuel vent, fuel tank pickup, racor fuel water separator.

Things I have not ruled out - fuel pump, inline filter (should have removed the screen as a test at the lake but forgot), & carbs.

Question for my internet mechanics - could trash in carbs or torn carb gasket cause these types of symptoms? I wonder if it is sucking air through the carbs?

Thanks very much guys!

[jjjtronics]

Try this; using a piece of clear fuel line, adapted inline with the fuel line, look for air bubbles running along with the fuel flowing while the engine is at the failing rpm. If you see air bubbles, you have got a vacuum leak somewhere, and that will make your life misserable.
I had a VERY similar problem once, using this clear line method, found a microscopic pin hole in the aluminum fuel pick up tube in the tank.
Remember that thanks to whoever made it a design-rule-law, outboards run on a vacuum- type fuel system all the way up to the pump, which is mounted next to the carbs/injectors, that way there is never-ever pressure on the fuel lines from the tank, which avoids leaks and fire hazards to almost zero. But vacuum leaks are hard to trouble-shoot, but, if the pums are pumping well ( checks with fuel pressure gauge ), and the fuel supply is good ( enough and free of bubbles ) your motor should run good, unless there is a problem with the motor itself.
If you have good fuel supply, I have cleaned my Yamaha`s carbs a couple of times and could help you out on that.

[Blue_Runner]

Thank you JJJ, good ideas.

I've cleaned my carbs with some help from a buddy twice. Might be time to try that agian. I will go ahead and get a carb kit to replace the gaskets. Last time in they were a tad brittle which makes me suspicious.