Engine shuts off

R

Roger K Sterling

Active Member
Oct 23, 2021
203
Boat Info
2000 Sea Ray 240 Sundancer
Engines
Mercruiser 5.0L, Bravo II, Thunderbolt V ignition
My engine is 2000 5.0 mercriuser with bravo 2 outdrive. I've changed the fuel water separator filter and the carburetor filter. It started and it idled for for 15mins. I shut it off and it's doing the same thing. It starts after I move the throttle into neutral but only for a few seconds.
 
You should have stuck with your original post, hard to remember what you have tried.
 
Roger, it’s only going to be fuel or fire. Meaning that either the engine isn’t getting the right amount of fuel or spark from the ignition.

Carburetors only need 3-4 psi of fuel pressure to operate. The next likely possibility is that the carburetor has a stuck needle valve and it’s causing the engine to flood. Another possibility is that the choke is not set correctly and it is also cause the engine to flood or be too lean on startup. If you haven’t messed with the mixture screws they are likely ok.

Once you’ve ruled out it’s not a fuel issue you’ll have to check the ignition side. Is there sufficient spark at the plug at the right time?

Check your distributor. The cap and rotor will wear over time. Check the spark plug wires. If they are old replace them. Over time internal wear and corrosion can cause electrical resistance to build in the wires and they will become less efficient at delivering a spark. Check your plugs for fouling. If they are ashy looking then it’s likely too lean and running hot. If they are oily then the piston rings or valve guides are likely leaking oil. If the are covered in black soot then the engine is running rich.

It’s also possible for the thunderbolt ignition module to be going bad in some cases. We can guess all day at what might be wrong with your engine but only specific diagnostics will actually help you find the fault.
 
If she starts every time without cranking and cranking, I’m betting a fuel issue. R U sure the fuel pump is good? She would start and run for a few seconds every time on the fuel in the carb, then starve out if pump isn’t working.
 
jmcdboater said:
If she starts every time without cranking and cranking, I’m betting a fuel issue. R U sure the fuel pump is good? She would start and run for a few seconds every time on the fuel in the carb, then starve out if pump isn’t working.
Click to expand...
He can test this out by putting a fuel source directly into the carb. I did that with a generator once and confirmed it was the pump.
 
Hoplite808 said:
Roger, it’s only going to be fuel or fire. Meaning that either the engine isn’t getting the right amount of fuel or spark from the ignition.

Carburetors only need 3-4 psi of fuel pressure to operate. The next likely possibility is that the carburetor has a stuck needle valve and it’s causing the engine to flood. Another possibility is that the choke is not set correctly and it is also cause the engine to flood or be too lean on startup. If you haven’t messed with the mixture screws they are likely ok.

Once you’ve ruled out it’s not a fuel issue you’ll have to check the ignition side. Is there sufficient spark at the plug at the right time?

Check your distributor. The cap and rotor will wear over time. Check the spark plug wires. If they are old replace them. Over time internal wear and corrosion can cause electrical resistance to build in the wires and they will become less efficient at delivering a spark. Check your plugs for fouling. If they are ashy looking then it’s likely too lean and running hot. If they are oily then the piston rings or valve guides are likely leaking oil. If the are covered in black soot then the engine is running rich.

It’s also possible for the thunderbolt ignition module to be going bad in some cases. We can guess all day at what might be wrong with your engine but only specific diagnostics will actually help you find the fault.
Click to expand...
 
Thank you for the response. This issue began when I was pulling out of the slip and as I started to throttle up the rpms would drop so I back off of about 30 seconds and then slowly throttle up. The rpms would then jump and from 2 to 3 knots to 5-6 knots. The next time out the engine stalled, wouldn't start and, I got towed in. Also prior to it stalling I ran it below a quarter tank. That why I started with the filters. I will begin the process of elimination based on your suggestions.
 
scoflaw said:
You should have stuck with your original post, hard to remember what you have tried.
Click to expand...
Adjusted fuel mixture screw, adjusted throttle screw, added sea foam all with good results in the past. Boat was running well. Then got sicknwith Covid so boat sat for two weeks. Took it out with 1/4 tank of gas. Next day these current problems started happening. Put 20 gallons in, sea foam. Still wouldn't start. Changed water/fuel filter and Carb fuel filter and it ran at idle for 15mins. Shut it off and it not starting or for a few seconds and then stalls. I've push throttle up to 4000 rpms and thn it still stalls out.
 
Kind of sounds like a fuel contamination or clog issue to me. When you put that 20 gallons in you probably stirred it up what was on the bottom of the tank. If you didn't let it sit for a few hours or so, you might have pulled some stuff in. Bypass the entire fuel system and run it off a clean/seperate can (not the boat's fuel tank) of fuel and see if that fixes the problem.
 
@Roger K Sterling if you still think it’s fuel it might be time to overhaul the carburetor. Could be a gunked up jet or the float ain’t set right or even could be a plugged up needle valve for the float.

With your added description of the erratic throttle I wouldn’t rule out an ignition system issue. When was the last time it had a proper tune up? New plugs, wires, cap, rotor and timing checked? If it’s been a while do that too. Look at the plugs and tell us what you see. There is a fair amount of information on what’s going on in the combustion chamber that can be gleaned by the condition of the plugs.
 
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