Stalling When Over 1000 RPM

[mhbt]

Hello everyone, I have a Bayliner with a MerCruiser 3.0L TKS motor. I just finished replacing the trim limit switch and sender after bringing it out of winter storage (failed at the end of last year) and got it on the water for the first time this season. The boat starts up great idles and moves in gear while in a no wake zone without increasing any RPMs. As soon as the throttle is moved to take the motor over approximately 1000 RPM, the motor immediately dies. This happens whether in gear or not in gear. If you repeatedly rev the engine while not in gear using the accelerator pump to shoot fuel down the carb, the engine will rev like normal up to normal RPM's but as soon as you stop constantly revving the engine and don't take the throttle back down to lower than 1000RPM (just above idle) then it immediately dies. If you return the throttle back down to neutral after your repeatedly keep revving it, it usually just sets back into normal idle speed and stays running.

I am wondering if anyone has any advice on what might be causing this? The boat was put into storage with a full tank of fuel with stabilizer in it. It seems like it is almost starving of fuel as it will run up the RPM range when you repeatedly revving the engine by actuating the accelerator pump. Any thoughts on this would be appreciated.

Thanks in advance!

 

[alldodge]

I would start with checking fuel pressure (3-7 psi) and then pull the carb and take it apart for cleaning

 

[wellcraft-classic210]

Hi
Sounds like a classic fuel supply issue. Probably Debris in carb float bowl or passages ( could also be corrosion if bad fuel was left in the carb )



I would suggest --

Pull the carb and clean all parts & ALL passages with carb cleaner and compressed air. ( If you see debris in the bottom of the float bowl that's a big sign of an issue )
Get a rebuild kit and install new gaskets at reassembly.

Good fuel filtration is the key to preventing recurrence if its caused by debris. Replace any filters if you have not done so recently and ensure whats their is adequate. Hopefully you have 1 that looks like an oil filter just before your fuel pump.


FYI -- When you engine goes from idle to over 1000 rpm's the fuel starts being delivered through the Venturis ( works like an airplane wing to create a vacuum and pull fuel ) and through different passages in the carb. The entrance to those passages are under 1/8 Dia and can be blocked easily. Smaller debris can enter and block the passages internally as well.
--You can often see fuel being delivered trough Venturi's when looking down the barrel on a carb that is operating properly // The idle circuits see more vacuum when you throttle plates are closed which is why they only work at idle-- The idle circuit will have adjustable screws to control fuel volume. The Venturi fuel volume is controlled by the hole size in the brass (jet) Orifice at the passage entrance on the float bowl.


If I missed anything I am sure someone will be along to help.

 

[mhbt]

Thank you for the thoughts. I pulled the carb off and sure enough there was debris and also a bit of corrosion on the bottom of the carb. Unfortunately, there is no factory fuel filter, other than the inline filter at the fuel inlet to the carb, on this boat. I will be looking to add one in the future. Despite the fuel stabilizer that was put in and circulated through the system before storage last fall, it looks like some of the fuel has gone bad. Such poor fuel quality these days.

I have taken the carb apart and blew out the passages with carb cleaner and compressed air so hopefully that should rectify the issue. All 3 local boat dealers did not have the rebuild kit (in fact they said they couldn't find a kit that Mercruiser made, just each individual components) so I cleaned out the jets and such and just bought a gasket kit as they had one of those. My next question though is that it appears that there are two base gaskets that are included with the kit, both are rectangular but one has a rectangular opening, and one has two circular openings (one for each barrel). My gaskets ripped when taking them off but it appears that mine had both of them on the base (circular center one on top and the rectangular one on the bottom) meaning that there were two gaskets on the base? Is that correct? This is the first time the carb has been of since factory but this seems odd to me. Usually you don't put 2 gaskets back to back and the fact that the circular one wouldn't have any support under the middle and overtime, when it dries out, could potentially break off and get sucked right into the intake manifold! I have attached an image of the two I am referring to. I have been looking in the service manuals but no luck.

Does anyone know for sure what the correct gasket(s) are to mount the carburetor to the intake? I want to ensure I do this properly. It is a 3.0l motor with the TKS Mercruiser carburetor on it. Any help is appreciated. Thanks again!

 

[alldodge]

Have seen many use both and its mainly because they came in the kit and the previous owner didn't ask and just used both. Use the one that matches the intake manifold.

 

[Scott Danforth]

. Despite the fuel stabilizer that was put in and circulated through the system before storage last fall, it looks like some of the fuel has gone bad.

fuel stabilizers only extend the life of fuel between 3-6 months.

E10 fuel life expectancy is based on many environmental factors (temperature, humidity, etc.) and will last about 3 months from the time it leaves the refinery before the ethanol starts to oxidize

E0 can be stored at low temp / low humidity for about 6-9 months (even though sunoco claims 12 months)

since 3.0 liters are entry level I/O motors, they are not rigged with a fuel/water separating filter from the factory. spend the $30 on a fuel filter kit.

 

[wellcraft-classic210]

Sound like your making very good progress !!!

This may be old news but -- Be sure to get the inside of the card as clean as possible. Card cleaner does not typically dissolve corrosion oxides ( often seen as green or white in color ) That can often be dissolved in overnight soak in white vinegar or similar agents.

And I would also suggests you add the fuel filter before restarting the engine if possible to prevent debris recurrence as the tank and any lines ( especially metal ones ) could have more crud in them from the bad fuel.

 

[mhbt]

Okay thank you again for the comments. If I use one gasket instead of the two I wonder if that would mean the mixture settings and such will be all out of line and needs to be all be readjusted? I wonder if I should just put two of the same gaskets on in stead of two different ones. I have also heard that you can get thicker gaskets through Merc. dealers as well. Just wasn't sure the best option or why two would have been used from the factory?

Also, does the fuel water separator act as a fuel filter as well or should I use both?

Thanks again everyone!

 

[alldodge]

No difference in fuel ratio

Yes, the separator is a fuel filter which helps separate water from fuel