Won't start after running fine all day on the lake.

[roblga]

My 1988 V6 merc 4.3 carb'd motor (140 hrs) takes everything we give 'er all day on the water, and when comes time to head to ramp recently - starts and idle fine, but as soon as you give the throttle a push it dies - no sputter, nothing. After we sit for a little while it seems flooded, almost turns over but never does, until today. I pulled off the spark arrestor and the choke was wide open - It kinda took a tug, but when I flipped it mostly closed - the motor started and we idled in gear to ramp.
Last week I pulled some gas out of the tank and found some separation, drained it and replaced fuel/water filer. Put in fresh high octane today and still died at acceleration on the water. Thanks for suggestions.
Rob

[mmwjr]

140 hours on a 1988, is that the original engine? You must spend a lot of time on the hook.

If there is phase separated gas as you stated the entire tank must be drained and disposed of, adding hightest will not fix bad gas. Try removing the fuel filter if you have the spin on type and pour the contents into a glass jar to look for water and phase separation.

[speedysprocket]

Maybe time for a carb rebuild...
Gas these days sucks. I rebuilt my carbs over the winter. Added gas to my empty tank between February and June. I ran one engine for 20 minutes on Tuesday. Put it in the water Friday and that engine refused to run. Opened the carb and gas had gelled in the bottom and clogged the jets. Opened the other one to clean it and it was full of sediment too.

[ss3964spd]

Sounds a whole lot like a bad accelerator pump to me.

When the engine is at idle the throttle is just barely open and the engine is running on the carb's idle circuit. Engine vacuum is high. When the throttle is opened there is a rush of incoming air (and thus a marked decrease of vacuum) which will make the A/F ratio go very lean unless there is a corresponding addition of fuel. That's what the accel pump in the carb does, it provides the necessary momentary shot of fuel to compensate for the increased air flow to cover the transition from the idle circuit to the main metering circuit. If the A/F goes lean too quickly there isn't enough fuel in the mixture to burn - engine simply stalls.

Pull the flame arrestor off the carb. With the engine off, open the choke and look into the carb while someone moves the throttle forward. You should see two small jets of fuel being squirted into the carb. If you don't, either the carb is empty or the accel pump is bad.

[roblga]

Thanks to all -
It's original owners had the boat mostly stored due to injury. I have had it 4 seasons and it's has been a jewell for the family. Until now. But hopefully minor maintenance.
I did drain the tank down to the last a week ago -
No separation from current filter.
I will get my next look at it next weekend and will pass on more -
Carb rebuild is how difficult?

[shrew]

Carb rebuild is easy, but its also cheap.

[speedysprocket]

If you've never touched the carb, it's certainly time. Not really hard, just a bit tedious with all the small pieces. Take your time the first time so you don't lose anything or forget to put it back in on reassembly.