Fuel problem, please help.

[Blue_Runner]

2004 Yamaha 150 carbed 2 stroke.

Above 4500 RPMs the fuel flow cannnot keep up and primer bulb starts to go soft allowing the motor to cut out. Runs smooth as silk anywhere below that. At 4500 and above someone can squeeze the ball and the motor will not cut out.

Couple things - installed a new primer bulb to be sure it wasn't that. Tank pickup seems to be free flowing and clear of obstruction. Racor F/W separator a little over 1 yr old. In-line filter seems fine, clear from obstruction and trash.

So, what could it be other than the fuel pump? I'm going to go ahead and replace the 2 filters anyway, but don't think it is going to help.

[Cam]

Sounds like a hose is collapsing on you. Have you checked the tank vent for a partial obstuction. Try running motor on a seperate line/tank and see if that solves the problem. Happened to a friend of mine and it turned out the inside of the fuel hose was collapsing under high RPM's. Check the obvious/cheapest things first.

[Blue_Runner]

Oh yeah, forgot to mention, checked the tank vent - no obstruction whatsoever.

I agree, I should run it on a separate tank and see what happens. If it were a line collapsing it seems I would have trouble priming the ball while my buddy is running it above 4500? I'm able to keep up and it doesn't "feel" like a fuel line problem.

[Cam]

I saw the fuel line that collapsed on my friend after he replaced it. It seemd like the fuel line had a bladder in it (a hose within a hose). some parts were still intact while a small portion of it was not. That was the part that gave him the problem. Running on a seperate line/tank is the way to go now to eliminate engine itself as being the problem. Good luck!!!!!!

[Blue_Runner]

Thanks Cam! I agree with you. I'll do that this evening.

For now, let's pretend I do that and still have the problem - what comes next?

[Destroyer]

Buy a Honda?


(Sorry, couldn't resist)...I'll keep quiet now..

[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!

[bradford]

Originally Posted by Blue_Runner

Thanks fellas!

* tank vent is clear. I can blow into the tank.

I wanna see pics.