Moderated Discussion Areas
  ContinuousWave: Whaler Repairs/Mods
  Mercury 50-HP FourStroke Stalls

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   Mercury 50-HP FourStroke Stalls
Andy321 posted 04-06-2015 05:17 PM ET (US)   Profile for Andy321  
I have a 2006 Mercury 50-HP FourStroke EFI Bigfoot engine. The only water-fuel separating filter is under the cowling and has a translucent bowl. I noticed that this bowl is never full of fuel when running. Sometimes it appears that there is little to no fuel in the bowl, but the engine is running. The primer bulb pumps up firm and the bowl is full when pumped firm. The engine runs great at idle and above 2000-RPM, but won't run smoothly between idle and 2000-RPM, stalls when the engine speed is decreased quickly, and sometimes stalls when slowly decreased below 2000-RPM to idle. Should the bowl be full at all times when the engine is running? If so, any idea what my problem is? The filter cartridge has been changed.
Phil T posted 04-06-2015 07:07 PM ET (US)     Profile for Phil T  Send Email to Phil T     
The bowl does not have to be full. How long have you owned the motor? Maintenance performed last year? Have you changed the spark plugs in the last three years?
Andy321 posted 04-07-2015 07:53 AM ET (US)     Profile for Andy321    
I have owned [2006 Mercury 50-HP FourStroke EFI Bigfoot engine] for two years. I believe the spark plugs were changed just before I purchased it. The engine oil and filter were changed, lower unit oil was changed, and fuel-water filter cartridge changed last fall. I live in Texas so the boat gets used all year, but not much for the previous three months due to the unreliability of its performance. Would spark plugs cause poor performance at 1,000 to 2,000-RPM but good performance below and above this speed range?
Phil T posted 04-07-2015 01:07 PM ET (US)     Profile for Phil T  Send Email to Phil T     
It does not read as though spark plugs are the cause. Changing them is a general indicator of the level of maintenance.

Does the motor run for long periods of time at idle or speeds under 4000-RPM, including hull speed?

EFI motors help narrow running issues down to a few areas. I suggest the engine's poor operation is related to one or more of the following:

--dirty vapor separator tank (VST)

--clogged low speed fuel injectors

--dirty old fuel residue.

Personally, I would replace all the fuel filters, clean and service the VST, and run a tank or two of fuel with an additive like Seafoam or similar.

Andy321 posted 04-07-2015 03:38 PM ET (US)     Profile for Andy321    
Thanks for the input Phil. Yes, the engine will run indefinitely and smoothly at idle and above 2,000-RPM, and below (or above) 4,000-RPM. I am not sure what hull speed is. I don't take the boat out because of the stalling; it is somewhat dangerous to lose all power suddenly when I try to throttle down.
jimh posted 04-10-2015 01:24 PM ET (US)     Profile for jimh  Send Email to jimh     
Remove the spark plugs. Check their appearance. They should not be wet or full of carbon or fuel residue. Check the spark gap on the existing spark plugs now. Plugs with a spark gap that is out of tolerance can cause problems when the engine is trying to accelerate. I became sensitive to this when owning an older outboard with a very strong spark that eroded the spark electrodes rapidly. I could tell when the spark gap on the plugs had eroded and become too large just from the response of the engine under acceleration.

The notion that your engine stalls mainly when decelerating is odd. It sounds to me like perhaps the fuel-air mixture is too rich and the mixture in the cylinder won't combust.

I don't endorse using fuel additives other than those recommended by the manufacturer. Mercury has three-tiers of products for treating the fuel system.


Of these, the progenitor of the naming seems to be QUICKLEEN, a product that has been around for a while. The other two products may be re-branded versions of legacy products. We look very briefly at all three:

QUICKARE is intended as a routine fuel treatment to be used in normal operation. It is to recommended to "add to every fill-up." It contains stabilizers.

QUICKLEEN is intended as a non-routine treatment when needed. This product has no stabilizers.

QUICKSTOR is intended to preserve fuel quality over long storage periods.

In addition to new names, the product packaging has been changed. Previously the plastic bottle was typically black and opaque. The new branded products are in clear plastic bottles. This may be a reaction to some incidents where sediment was reported in fuel treatment products, only discovered after use due to the opaque bottles. fuel-care-system/

Since you may be having fuel related problems, try using QUICKEN engine treatment:


Marine Grade Product

--specially formulated for gasoline used in 2-cycle and 4-cycle marine engines.

--Mercury® Quickleen Engine Treatment is three performance enhancing treatments in one:

----Detergent to clean combustion chamber deposits
----Dispersant to prevent formulation of future deposits.
----Rust inhibitor to prevent corrosion of internal ferrous metal surfaces.


---- Add one ounce of Quickleen™ per six gallons of gasoline at each tank fill throughout the boating season.

----See your engine service and maintenance manual for specific applications and maintenance schedules.

--Keep your engine running longer and stronger with Mercury® Precision Parts.

Part no. 92-802877A 1

Again, I don't recommend you approach fuel treatments by becoming your own fuel chemist and buying various off-the-shelf brands of chemicals to mix in your own proportions with your gasolie fuel. Follow the guidelines of your engine manufacturer.

After you run a tank or two of fuel treated with QUICKEN, replace the spark plugs with new plugs.

Andy321 posted 04-21-2015 12:51 PM ET (US)     Profile for Andy321    
Mercury responded to my inquiry. They said the symptom of stalling when decelerating is most likely due to an incorrect setting of the idle air control valve. They said this setting is done electronically using their software and has to be done by an authorized service center. Do you have any comments on this? I don't have an easy or inexpensive way to get the boat to a service center.
jimh posted 04-21-2015 02:30 PM ET (US)     Profile for jimh  Send Email to jimh     
I wonder why the setting of an electronically controlled air valve would change over the life of the engine. Why would it be something to adjust with software as the engine is used? If the engine has always had the problem described, it seems reasonable to think the setting has been wrong from the factory.
Andy321 posted 04-24-2015 03:13 PM ET (US)     Profile for Andy321    
Yes, I wondered the same things; that is why I asked for your knowledgeable opinion. The motor was working fine until about 3 months ago when it suddenly developed the problem cited. It still starts immediately and runs fine at idle and above 2000 rpm.
jimh posted 04-25-2015 10:34 AM ET (US)     Profile for jimh  Send Email to jimh     
I can't offer any knowledge about how a Mercury 50-HP FourStroke engine controls the setting of its idle air valve by software contained in its engine controller. The suggestion you received from someone at Mercury that to provide a remedy to the running problem of the engine--its frequent stalling--there must be some electronic manipulation of the action of the electronic controller just seemed odd to me.

Typically many engines have an idle air bypass circuit, which, as I understand it, is a path for air to reach the fuel induction path to the combustion chamber, even when the throttle plates of the main air path are completely closed.

By using the term "idle" I presume it refers to the speed of the engine at minimum throttle, that is, when the throttle is closed all the way.

By using the term "valve" I presume that the air path is controlled by some sort of valve that regulates the amount of air that can flow in this idle air bypass path.

By suggesting that some modification must be made using electronic communication between the engine controller and some remote terminal or diagnostic hardware, I make the inference that the control of this idle air bypass valve must be in some way dynamic or proportional, and the engine controller must provide an electrical signal to the valve to make it open or close at the proper times.

But what makes no sense to me at all is the notion that the method of controlling the idle air bypass valve must be changed. Perhaps what the advice you have received is really trying to say it this: there was a defect in the way this valve was being controlled in the original settings embedded into the firmware of the engine controller, and this defect causes the engine to stall in the conditions you experience, and there is an improved version of firmware that compensates or corrects or improves the control of the valve to prevent the stalling.

That is just my guess. Why don't you ask the dealer about this. If there is a firmware update that corrects this defect, and if your engine is stll in the warranty period, maybe you can get the repair of the original defect in manufacture of the engine corrected or remedied under the terms of the warranty.

jimh posted 04-25-2015 10:41 AM ET (US)     Profile for jimh  Send Email to jimh     
If the onset of the problem was only three months ago, and if before that the engine did not have this stalling problem, it seems really unlikely that the remedy must be in software. Maybe there is some obstruction in the idle air bypass path, such as a hose that has become blocked. Maybe there is a failure of the electrical device that controls the valve; it might not be responding any more to the electrical signal it gets from the controller. It could be something as simple as a loose electrical connector at the control valve.

But it seems odd that the remedy to this would be in changing the firmware in the controller.

I think many first-level technical support representatives tend to throw out recommendations or solutions to problems that are more or less stock answers. Those people might not possess the real knowledge or experience or familiarity with the products they support to the degree necessary to be able to resolve any problem encountered over the telephone.

jcdawg83 posted 04-30-2015 02:49 PM ET (US)     Profile for jcdawg83    
I think the default response to inquiries to the manufacturer is ALWAYS "take engine to an authorized service technician for diagnostics". There is no way they are going to cut their dealers out of the money loop by telling you "oh, that's a simple fix, lightly tap the left side of the fuel pump with a small hammer three times and you will be fine".

Post New Topic  Post Reply
Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.