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140 Mercruiser dies after running a while.

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Bob Komischke

New member
Hi Folks! I just found this forum, and I'm hoping to get some help diagnosing a problem with my 140 MerCruiser sterndrive. It's a 1973, in a Larson All American. The boat was my dad's, who passed away a couple years ago. The boat had been garaged, unused, for quite a few years, and is like new, only 275 hours on the motor. I brought the boat in to a mechanic last year to go over the engine after all that sitting. It starts great, runs smooth, but here's what's started happening. After I'm cruising for a while, say 15-20 minutes, not wide open, maybe around 3200 RPM, the engine will start to sputter (almost like it's running out of gas), and eventually die. I can get it to start again, but it won't keep going. If I let it sit for a bit, it'll start, and run for a while, and then quit again. If I let it cool off completely, it'll start right up again, run good for a while, then the same behavior. It seems like something is happening once the engine runs long enough and something gets hot enough. I'm hoping this sounds familiar, and someone can suggest what needs to be fixed that I can do, and avoid pulling the boat out of the water and hauling it back to the mechanic. Any ideas? Thanks:)
 
Ignition coils will fail when they get hot.try taking the High Tension lead out of the middle of the distributor cap,the one from the coil, [when the engine has died] and hold it about a quater of an inch away from an earthing point,and wind the engine over and see if you get a healthy blue spark.be careful of any petrol vapours though.If the spark is weak,or intermittant,try a new coil.if its strong and blue,pull a spark plug and see if its wet with fuel or dry.try pumping the throttle,and look down the carbie throat to see if any petrol is squirted into the venturi.that will tell you you have petrol in the carbie.But only do the petrol test when the engine first cuts out,as the carb will fill via the fuel pump,while your checking for spark.make sure you put the aircleaner back on before checking for spark.I personally am a great believer in renewing those older type coils anyway,as 1973 to 2011 is a long time to be pumping out 25 - 40,000 volts
 
Welcome aboard !

Is the vent clear ?

When it happens pop open the gas cap, see if you hear air rushing in.

I'm Backkkkkkk !
 
Thanks for the reply. I've never noticed air when I fill up, but I can check right when this is happening. I 'spose if it is developing a vacuum it would disapate slowly and that could explain why it goes away after things sit a while.

chiefalen said:
Welcome aboard !

Is the vent clear ?

When it happens pop open the gas cap, see if you hear air rushing in.

I'm Backkkkkkk !
Click to expand...
 
I wondered about the coil myself. Good to get a possible confirmation on this suspicion. I'll investigate and report back. Thanks.

budgie14 said:
Ignition coils will fail when they get hot.try taking the High Tension lead out of the middle of the distributor cap,the one from the coil, [when the engine has died] and hold it about a quater of an inch away from an earthing point,and wind the engine over and see if you get a healthy blue spark.be careful of any petrol vapours though.If the spark is weak,or intermittant,try a new coil.if its strong and blue,pull a spark plug and see if its wet with fuel or dry.try pumping the throttle,and look down the carbie throat to see if any petrol is squirted into the venturi.that will tell you you have petrol in the carbie.But only do the petrol test when the engine first cuts out,as the carb will fill via the fuel pump,while your checking for spark.make sure you put the aircleaner back on before checking for spark.I personally am a great believer in renewing those older type coils anyway,as 1973 to 2011 is a long time to be pumping out 25 - 40,000 volts
Click to expand...
 
See when it happens you have to know whats missing fuel, fire or air or compression.

You messing fire or fuel in my inexpert opinion.

You tell us what we will tell you how to fix it.
 
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