9.9 stalling

[mycoho11]

I have a T9.9elrs that enjoys stalling. The engine will start up right away, sometimes run perfect for over ten minutes and then stall like it was turned off. Most times it will start right back up. At mid throttle it will run fine then will rev up or down on its own? At full throttle is does not run long or even make it there.When the issue first started, I could keep it running by pumping the primer ball, now it does not. So far the fuel pump has been rebuilt, new tank,lines and primer ball (even the engine fitting has been bypassed), carb looked clean but was cleaned 3 times anyway,needle valve replaced, prime start replaced, coil replaced, plugs, fuel filter. The motor is not overheating or sounds unusual when running. My gut says to me carb, sticking float maybe. But I am missing something? I have owned it since 94 and have never had a problem till now.

[boats.net]

It sounds like the carb is dirty, low speed jet may still be clogged.

[TownsendsFJR1300]

I have a T9.9elrs that enjoys stalling. The engine will start up right away, sometimes run perfect for over ten minutes and then stall like it was turned off. Most times it will start right back up. At mid throttle it will run fine then will rev up or down on its own? At full throttle is does not run long or even make it there.When the issue first started, I could keep it running by pumping the primer ball, now it does not. So far the fuel pump has been rebuilt, new tank,lines and primer ball (even the engine fitting has been bypassed), carb looked clean but was cleaned 3 times anyway,needle valve replaced, prime start replaced, coil replaced, plugs, fuel filter. The motor is not overheating or sounds unusual when running. My gut says to me carb, sticking float maybe. But I am missing something? I have owned it since 94 and have never had a problem till now.

First off, when the carb was cleaned, were the idle and main jets actually REMOVED FROM THE CARB BODY? There are sometimes very small holes in the sides of the idle jet that you cannot see unless the jet is removed and visually inspected (see sunlight thru). The holes are small enough, I've had to use a wire brush wire to clean them as a needle was too big.. On the bench, you can attach fuel line to the carb, use a small auxilary tank and see if fuel stops and starts when you manipluate the float up and down. You can even use water for safety, just make sure its all dried before re-assembly. Some carbs, it makes a difference if the float goes on first, then the gasket and vs versa. My neighbor mixed this up on one of 3 carbs on 200 HP until I found it..

Check ALL your O-rings in the fuel system, especially the engine fuel filter and if you have a transom mounted filter. Make sure your float itself is NOT LEAKING/holding in fuel.

It sounds like your sucking air into the system.. When it does stall, turn off the engine.

There should be a drain screw for the float bowl. Bring a catch can (I use a clean tuna fush can), open the drain screw and see if ANY FUEL COMES OUT. If its about dry, its a fuel delivery problem. If its dry, leave the drain screw loose and prime the bulb, see if it pumps fuel up thru to to the carb.

Rising RPM's before stalling, its leaning out(running out of fuel). No full throttle again points at a dirty main jet, or fuel delivery. If the idle jet is clogged, it will not idle, period..

Something else to look for, ethonol will destroy old fuel line. I've had the fuel line, internally disintegrate from the transom fuel filter to the engine fuel filter on the engine(that's from 2006). If your Yamaha fuel filter is similar to mine, there is an o-ring that seals the see thru filter. The ethonol fuel will expand the plastic and not allow the see thru housing to fully seat with the o-ring (major air leak).

Check / replace any fuel lines in the engine fuel system related as the engine is about 8 years old and the ethonol crap helps deteriorate them. I would strongly suggest using some "Chevron techtron" fuel additive as well. Its a fuel system cleaner and helps stabilize the fuel...

Good luck

[mycoho11]

Thanks for the reply Townsends. I like the idea on checking the float. Yes the jets were removed, cleaned, and inspected. Like I stated the carb looked very clean when first opened up, I actually was disappointed not to find crud anywhere in the carb when it was completely disassembled for cleaning. Not too many o rings on this carb. I did use just a carb spray can for the cleaning, one without alcohol, in all the spots I could find. I read in a older post about soaking in denatured alcohol....is that safe to do?
The engine does not increase rpm's before it stalls..but just like turning of the key. It starts right back up so I think fuel is getting there.
If the carb/jet was dirty or the engine was sucking air into the fuel why would it run so erratically? What about the accelerator pump? How is that checked and what does it do. Mine visually looks fine but it is rubber. I don't mind pulling the carb again but I was looking for suggestions as to what else could cause intermittent stalling, like some sensor

[TownsendsFJR1300]

Thanks for the reply Townsends. I like the idea on checking the float. Yes the jets were removed, cleaned, and inspected. Like I stated the carb looked very clean when first opened up, I actually was disappointed not to find crud anywhere in the carb when it was completely disassembled for cleaning. Not too many o rings on this carb. I did use just a carb spray can for the cleaning, one without alcohol, in all the spots I could find. I read in a older post about soaking in denatured alcohol....is that safe to do?
The engine does not increase rpm's before it stalls..but just like turning of the key. It starts right back up so I think fuel is getting there.
If the carb/jet was dirty or the engine was sucking air into the fuel why would it run so erratically? What about the accelerator pump? How is that checked and what does it do. Mine visually looks fine but it is rubber. I don't mind pulling the carb again but I was looking for suggestions as to what else could cause intermittent stalling, like some sensor

I've never soaked a carb, so I don't know about the alcohol. I do know they make a carb cleaner that you dip the carb body into.

As for the/a accelerator pump, I wasn't aware the 9.9 had one.

The older cars with carbs, Harleys with a Mikuni carb has them(some other as well). Basically what the accelerator pump does is pump a small stream of fuel down the throttle body. You will literally see (if its working properly) fuel spray out when you open the throttle.

I have to doubt you have one but I could be wrong. The rubber cup attached to the accelerator pump usually fails with time and will NOT pump fuel causing a bog. If you accelerate slowly, you don't even need the accelerator pump.

When the engne stalls, can you pull the carb bowl drain plug and see how much fuel comes out? You can also by pass the fuel pump and hook up a small auxilary gas tank (I use an extra lawn mower gas tank with an on/off valve) held above the engine(gravity feed) plumbed into the carb. NOTE, the fuel pump will still want to pump (if its working) so hook up a line into another can and see if it indeed IS PUMPING. Run the engine on the auxilary tank and see what happens. if it runs good, your problem is BEFORE THE CARB somewhere. If it still runs crappy/stalls, its likely IN THE CARB (crap stuck inbetween the carb needle seat, etc).

Not being able to full at full throttle sounds like a fuel delivery problem, its not getting enough fuel up/thru the main jet. A leaky O-ring/connector will cause the fuel NOT TO FLOW FULLY to the carb...

Something else, with the smaller engine, the carb body may have some very small holes in the throttle body just about adjacent to the throttle butterfly. If yours has these, make sure they are clean (as they can varnish up). I would strongly suggest using brake cleaner vs carb cleaner as its not quite as aggressive on rubber parts. Make sure when spraying into one of the small holes the brake cleaner actually goes thru fully.

If your spraying something without rubber seals, the carb cleaner is fine.

Your just going to have to eliminate things one at a time.
__________________________________________________ ________________________________
What year/model is your engine? I just looked up a 2000 9.9 and there is NO accelerator pump

( http://www.yamaha-motor.com/partview...px?ls=outboard ) The parts fisch of the carb shows the correct assembly (parts wise) once brought up and zoomed in.


Good luck...

[mycoho11]

A t9.9elrs is a 1994 model. My service manual mentions the accelerator pump..in the diagram for the carb I am guessing it is talking about #30 "diaphragm assembly". The rubber disc has a metal center and when the throttle is advanced a cam/lever presses on it. It can not actually "pump" since it moves in relation to the throttle but it must create a pressure or vacuum. I'll give your gravity fed carb a try.

[99yam40]

probably better to test things with a pressure vacuum gauge and a piece of clear tubing to see if there is a restriction, pump functioning properly, or sucking air

[TownsendsFJR1300]

A t9.9elrs is a 1994 model. My service manual mentions the accelerator pump..in the diagram for the carb I am guessing it is talking about #30 "diaphragm assembly". The rubber disc has a metal center and when the throttle is advanced a cam/lever presses on it. It can not actually "pump" since it moves in relation to the throttle but it must create a pressure or vacuum. I'll give your gravity fed carb a try.

Looking at the diagram, if part # 39, "starter rod" attaches to it, then to the "starter set"-solenoide, I suspect its not an accelerator pump but a diaphram to start/enrichen (choke) the engine when cold. In either case, it shouldn't have any tears or cracks in it.

As stated earlier, gravity feed fuel to the engine, catch fuel from the fuel line (check and make sure its pumping fuel in a container) and start narrowing things down.

Good luck.