Engine dies after 30 seconds

[Samraz]

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.

 

[Droid]

Maybe it's getting too much fuel?

 

[Dieter]

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.

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?

 

[Samraz]

Maybe it's getting too much fuel?

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.

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?

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.