Stalling

[eeshaw]

Need some guidance/help.

I have a 2006 Yamaha 40 four stroke that stalls when I put it in gear and try to throttle up with it. It pees a good stream while idling and starts right up but will stall if I try to increase the rpms. I let it warm up for a few minutes, I've put fresh gas in it and new plugs. I checked the gap and they're the the same as the ones I removed, .030 inch. I've tried looking on line to see if there's a water seperator for the engine and haven't seen one referenced anywhere. I'm at a loss and I don't know what to look for to troubleshoot this problem. Normally I'd just take it to a dealer but the closest one is about 50 miles from me. I am mechanically inclined and know the basics of combustion theory but I'm not familiar with outboard engine operation. I would remove the carbs and check the jets to make sure none are plugged but I don't have any way to synchronize them if I took them apart so I've left them alone. I would think it's probably something simple that I'm missing. Is there a manual that I could reference for this problem?

Is anyone here that might know of what I should look for to address these problems? Any help is appreciated. I think it's kind of ridiculous that a Mercury dealer can't work on my engine, or any engine that isn't Mercury. I guess that it's just another way to gain market share. Thanks for any help folks.

 

[JL8Jeff]

I think there is an issue with the Yamaha 40 4 stroke and I forget if it's injectors, carbs or fuel pump. My cousin had problems so I'll ask him.

On my Mercury 2 stroke, I had problems where the O-ring on the fuel connector was letting air get into the fuel line and it would bog down with any amount of throttle. If you have clear fuel lines or a clear filter, you might be able to see if there are any air bubbles getting in.

Update: My cousin said they had a blockage in one of the 4 carbs and they kept running Seafoam through until it cleared out. I know that motor is still running good now, one of their neighbors bought it and runs it on his pontoon boat.

 

[Scott F]

Have you checked the fuel filter?

 

[Pappy]

^^^^Fuel filter will not cause stalling just off idle.

Chances are you have a dirty idle circuit in one of more carburetors.
They are adjustable but normally have a plug over the top of the idle adjustment screw.
No guarantee an adjustment will do the trick but may be worth a try.

 

[CedarRiverScooter]

If you want to fix it yourself, buy a repair manual. Best money you will spend on the motor.

 

[eeshaw]

Thanks for the replies. I changed out the inline fuel filter today, still no improvement. I've made an appointment for the 18th to have it looked at. I just hope they're gentle! ha ha ha I figure it's something carb related, I don't think that it has injectors, but maybe it does. I'm going to look into a repair manual for it though. I've done simple maintenance on it like the water pump impeller, plugs, fuel filter and what not. Anyone know where there is a air filter for it? I looked at the carb situation today. Looks like a stack of interconnected carbs. I'm sure it would be real interesting to dig into it! It probably would never run again. I'm kind of at a loss as to why it would develop a issue. I NEVER run ethanol in it, ever.

 

[Pappy]

No air filters....not much dust out on the water!
Already mentioned that a fuel filter would not cause it to do what you are describing.

From the sound of it ....you need to have it done rather than tackle it yourself since you are not even sure whether it is injected or carbed.
As far as costs go prepare to absorb the cost of a complete carb repair, as in all carbs not just one. Hopefully you will have it at a place that has access to OEM parts and kits and will do the job right.
Non-ethanol fuel is better than ethanol enriched but can still cause issues if left for long periods of time.

 

[eeshaw]

Pappy, let me ask you this. If leaving old fuel in the engine isn't good is it acceptable to run it with the fuel line disconnected until the engine quits? I don't want to damage the engine by running it lean either.

 

[JL8Jeff]

Have you tried squeezing the fuel line ball when you start to give it throttle to see if it will keep running?

I had to rebuild the 3 carbs on my Mercury a few years ago. I think what happened was the ethanol in the fuel caused the inside of the rubber fuel lines to deteriorate and that clogged my filter. Not knowing this, I squeezed the ball too hard and blew out the filter and all the junk got into the carbs. I already had a paint can size of carb cleaner from NAPA when I rebuilt the Holley carb on my old Camaro so I ordered 3 Mercury rebuild kits and took each one apart one at a time and soaked them in the cleaner. I put the parts from the new kits in and put everything back together and just had to dial in the idle and mixture and it has run great since then. It does sound like you might have some dirt/gunk in at least one of your carbs and it probably needs to be soaked in the cleaner. I think the Mercury kits were around $35-50 so if your Yamaha has 4 carbs and the kits are $50 or more, add the time/labor for someone to take them apart, clean and reassemble and adjust, you might be looking at $500 or more (unless the Yamaha kits are a lot less).

 

[eeshaw]

Well, I have my kicker, a 9.9 Mercury hooked up to the gas tank up front and it runs fine. I thought, well, maybe it's not getting enough fuel since it's a 40 so I got a new tank out that I hadn't used and put a new ball on it and clear reinforced hose so I could see that it was actually getting fuel without any bubbles. Everything looked fine. I even increased the line size to 3/8 inch, mainly because that's what I have handy. Either fuel source, it runs fine until I increase the rpm. It acts like it's starving for fuel so it may be a problem with the secondary circuit. New tank, gas, lines and bulb along with a inline fuel filter to a distribution manifold. I even double checked that the bulb was oriented the correct direction, so I know this stuff isn't causing any issues.

 

[Pappy]

The information below will be assuming you (we) are starting with a well sealed engine with good compression, etc.

Guys - The sole purpose of a primer bulb and/or a fuel pump is to fill the bowl in the carburetor(s) until the float needle closes on the seat.....period. Read that sentence again! That is all they do.
Pour it into the fuel bowls by a bucket, gravity feed it from a tank higher than the carbs, use a turkey baster, put an electric fuel pump on it, etc. they all do the exact same thing. They fill the fuel bowl then sit their lazy mechanical butts around and wait for the fuel level to drop and fill it again, you get the idea.

The single exception that is seen fairly frequently is a ruptured diaphragm on a crankcase mounted fuel pump that will feed excess fuel to one cylinder and flood it. From what you are experiencing this is not happening to your engine.

Now, once the fuel bowl is full and the needle and seat is closed you can throw away your fuel filters, primer bulbs, fuel pumps, gravity feeds and whatever else feeds the carb(s). Say what???

It is the carburetor that runs the engine until the fuel level goes down, not the filters or pumps. The carbs run the engine and are in charge of running quality.

"Today's" carburetors normally have an idle circuit, an off-idle circuit, and a high speed circuit. Any or all of these circuits can experience issues and affect the running quality of the engine.
The idle and off-idle circuits are the smallest and most prone to blockage. These are the circuits that idle the engine and accelerate the engine until the high speed circuit tips in and takes over. There are overlaps between circuits as well but as long as you keep this in mind it should make troubleshooting a bit easier.
On multi-carbed engines the throttle linkage and ignition pick-up timing will also play a part in idle and off idle running quality. Always eliminate sync and link issues first before diving in to the next steps in solving running quality issues.

In this forum we try and offer as much helpful information we can that will not just suggest you replace and or throw parts at it until fixed.
Look for detailed explanations of the information being offered. This will help save time and expand your knowledge of how things work.

 

[eeshaw]

Thanks for taking the time to make your posts Pappy. I for one appreciate it. I have a degree in Mechanical Engineering and have worked as a machinist for many years. I've learned that there are things I'm comfortable doing and others that I'm not, due to lack of experience. Screwing around with my outboard is one of them. I wouldn't hesitate with a single cylinder to dive into it but learning to work on the fuel system for a multi cylinder outboard isn't a good place to cut my teeth by flying blind. It would get expensive real quick and like you stated, just throwing parts at it and hoping for the best is just poor strategy. Sometimes you have to pay for the expertise and this is one of those times.