Sputter and stall at High speed

[DeanBC]

Hi I have a 2001 mercury 125 outboard and it’s been giving me grief on and off for years. Usually the first several outings are great but with more use it starts to act up, usually at higher speeds. When it acts up it’s as if the motor isn’t getting gas and it sputters violently. Sometimes this can be managed by easing the throttle off and on. Other times it is unmanageable and does not recover and stalls after the violent sputters. I am always able to start it up easily and move very slowly after these incidents, sometimes, like today it even gets back up and running for a while . Anyone have any ideas?

 

[Scott Danforth]

When was the last time you serviced the carbs and fuel pump?

 

[roscoe]

What have you tried so far?
Anyone tinkered with the carbs or linkage?
How about the fuel lines from the pick up in the tank, to the final connection at the carbs, and all connections in between?

 

[DeanBC]

I had all carbs cleaned and the fuel pump rebuilt when the problem first started occurring but it’s still happening. I haven’t replaced any lines but I’ve tried to make sure the connections are all tight. Do think a faulty bulb in the fuel line could cause it? I

 

[444]

You need to have someone start pumping the bulb when it starts sputtering to see if it clears. Fuel line connections are clamped with gear clamps? Fuel filters have been changed? Fuel tank venting properly and not building vacuum in the tank?

 

[DeanBC]

I had someone pump the bulb yesterday when it was acting up and it didn’t help. In line fuel filter was replaced and I also added a water/fuel separator filter. Some of the clamps on the motor are just zip ties which came from the factory. Actually I think one of the littles hoses to a cylinder may not be great.

I can’t figure out why it can run perfectly for 30 minutes or more without issues and then gets worse and worse with more use.

i haven’t checked the vacuum issue in the tank, I guess I could try opening the gas cap periodically. It doesn’t screw shut just clicks open or closed.


thanks for you thoughts guys,

 

[bwguardian]

I'm having similar issued with almost identical motor I started a thread on here...

 

[DeanBC]

I just read your post. Sounds very similar. Did you resolve the issue?

 

[DeanBC]

Oh I see you just posted it today. Please let me know if you are able to fix it. I’ll do the same.

 

[frogseatflies]

Same problems here. Posting a video showing this problem in about this in about 30mins about my 6hp.

 

[frogseatflies]

Here's my post showing my similar problem in a real-world at-sea scenario.

 

[havoc_squad]

If this is carb outboard, then I suggest you break out some simple diagnostic tools. If this is fuel injected, you will need the electronic diagnostic program/tool to make sense of what is going on and then that will dictate the tools used.

1. Low pressure fuel pressure gauge, fuel T fitting, extra hose that fits on the outboard's fuel system, and hose clamps. The objective is to put this on to monitor fuel supply. You want the gauge to be on the line that goes to the carbs after the fuel pump, not before it.

If you're fuel supply starts to drop below the acceptable range at high speeds OR if an over pressure issue occurs, you'll know where to focus.

2. Timing Light. When aimed at the timing spot while the engine is underway with #1 spark plug used, this will show you the timing behavior AND it will show you the behavior of #1 spark. Once timing behavior is verified within spec per service manual, you can move the timing sensor to other spark plugs and see if a misfire occurs leaving an inconsistent gap of time before spark returns.

3. Spark plug socket and socket wrench to check the spark plug's colors to verify the cylinders are not running lean or very rich.

Time to get the detective hat out and get the outboard in a situation to act up with diagnostic tools ready to get data.