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Engine dies after 30 seconds

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Samraz

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My 1992 Mercruiser 140 engine is having a consistent problem. Starts cold runs great. About 30 seconds later it just cuts out and dies. Then it’ll start again but dies after about 10 seconds. It might start a third time but will die quickly and won’t start after that until sitting for a while.

I believe it is electrical because it happens when I manually pour fuel into the carb and because the accelerator pump in the carb always squirts fuel. Also, watching my spark plug tester, spark seems weak and inconsistent.

I was sure it was the coil so I replaced it. Same problem. I then replaced points, condenser, cap, rotor, plugs and wires. Same problem. I then tried two other coils. One just to see if the one I bought had a weird problem, and the other with internal ballast resistance. No change

Then, I bypassed the entire wire harness and wired new ballast resistor straight to the battery bypassing the instrument cluster, kill switches, shift interrupt switch. Everything. Battery straight to coil via resistor, and starter wire straight to coil for starting (which I remove as soon as it starts). Still no change. It dies after about 30 seconds. The battery is fully charged and alternator seems to be working well.

I am hoping this group of smart people might be able to help me.
 
Samraz said:
My 1992 Mercruiser 140 engine is having a consistent problem. Starts cold runs great. About 30 seconds later it just cuts out and dies. Then it’ll start again but dies after about 10 seconds. It might start a third time but will die quickly and won’t start after that until sitting for a while.

I believe it is electrical because it happens when I manually pour fuel into the carb and because the accelerator pump in the carb always squirts fuel. Also, watching my spark plug tester, spark seems weak and inconsistent.

I was sure it was the coil so I replaced it. Same problem. I then replaced points, condenser, cap, rotor, plugs and wires. Same problem. I then tried two other coils. One just to see if the one I bought had a weird problem, and the other with internal ballast resistance. No change

Then, I bypassed the entire wire harness and wired new ballast resistor straight to the battery bypassing the instrument cluster, kill switches, shift interrupt switch. Everything. Battery straight to coil via resistor, and starter wire straight to coil for starting (which I remove as soon as it starts). Still no change. It dies after about 30 seconds. The battery is fully charged and alternator seems to be working well.

I am hoping this group of smart people might be able to help me.
Click to expand...
Get a spark gap tester and test for spark when it won’t restart. You set the timing and dwell ? If you adjust the idle mix ont he carb in or out does that affect it?
 
Droid said:
Maybe it's getting too much fuel?
Click to expand...
I will consider that for sure. I have decided to rebuild the carb even though there are a number of reasons why I don’t think it’s fuel.
Dieter said:
Get a spark gap tester and test for spark when it won’t restart. You set the timing and dwell ? If you adjust the idle mix ont he carb in or out does that affect it?
Click to expand...
I will test the gap. The timing is good. I haven’t set the dwell but I’ve gapped the points and tested continuity while manual turning the engine and the points are at least set well enough that I wouldn’t think the original problem would persist without change. But maybe dwell would help. I’ll do that.
 
Samraz said:
I will consider that for sure. I have decided to rebuild the carb even though there are a number of reasons why I don’t think it’s fuel.

I will test the gap. The timing is good. I haven’t set the dwell but I’ve gapped the points and tested continuity while manual turning the engine and the points are at least set well enough that I wouldn’t think the original problem would persist without change. But maybe dwell would help. I’ll do that.
Click to expand...
Gapping points gets them close but need to measure and adjust with a dwell meter to really get it right. Its is what determines how much energy the coil makes before it fires so don’t overlook this critical step. Also when you change points timing can change some too.

What do the spark plugs look like? Might do a little more troubleshooting before tearing I into the carb, not that it will hurt to rebuild it but may introduce additional variables if not done right. I have gotten best results by cleaning carbs in a cheap ultrasonic cleaner from harbor freight. Defeinetly gets it cleaner than I used to by carb cleaner and compressed air
 
Engine starts fine cold. That's when choke is closed because it needs extra fuel. Each subsequent start has it die sooner. It sounds like after 3 cycles it must wait before it will start again. That's why I'm thinking too much fuel.

Answer these questions:
*Did this just start suddenly one day?
*Had you changed any parts or made any adjustments immediately prior?
*What brand or parts did you use? OEM or Chineesium?
*IF you leave the ballast bypass 12 volts on after engine start, will it continue to run? Don't worry about frying any components with the extra voltage for just a few minutes.

You say above:
"Then, I bypassed the entire wire harness and wired new ballast resistor straight to the battery bypassing the instrument cluster, kill switches, shift interrupt switch. Everything. Battery straight to coil via resistor, and starter wire straight to coil for starting (which I remove as soon as it starts). Still no change. It dies after about 30 seconds. The battery is fully charged and alternator seems to be working well."
This seems like you have tested electrical gremlins well.
 
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