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starts, runs, stops running. repeat

Old 09-05-2017, 11:51 AM
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Default starts, runs, stops running. repeat

Stock 7.4l carb mercruiser gen5
The port engine will start, idle and run fine in gear at various RPM's for 5 minutes, 15 minutes, whatever, runs normal then suddenly dies when being returned to idle and usually will not restart and run correctly. End up idling in on one engine twice this past weekend.
Back at the marina from cold the same port engine will start and die, won't idle or hold rpm if accelerated, never gets started correctly. But then suddenly it starts and run correctly. Very intermittent, thinking electrical and not knowing where to start. Plugs look good and is getting fuel.
Suggestions ?
Thanks, ed
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Old 09-05-2017, 01:41 PM
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Put a timing light on any plug wire. When engine won't run, crank. If you have timing light flash, rebuild the carb. If light is dead, ignition is intermittant.
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Old 09-05-2017, 03:56 PM
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check the cannon plug for corrosion ,i have seen this cause all kind of problems.
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Old 09-05-2017, 05:07 PM
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Originally Posted by dereknkathy
Put a timing light on any plug wire. When engine won't run, crank. If you have timing light flash, rebuild the carb. If light is dead, ignition is intermittant.
It will always fire, just won't keep running sometimes. Carb was rebuilt in June.
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Old 09-05-2017, 06:19 PM
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also could be the coil,ignition module.
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Old 09-05-2017, 06:26 PM
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Under $10 !
All parts stores have them:

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Old 09-05-2017, 06:29 PM
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You can find some of these under $30 or in your buddies garage free.

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Old 09-05-2017, 07:07 PM
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Originally Posted by SB
You can find some of these under $30 or in your buddies garage free.

starts, runs, stops running. repeat-s-l1000.jpg
Have them.
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Old 09-05-2017, 07:10 PM
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Originally Posted by mike tkach
also could be the coil,ignition module.
I have a spare coil so since it's a quick swap i'll try that first.
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Old 09-05-2017, 07:37 PM
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What is your serial number?
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