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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10600
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have 6hp model j6rcrm with weak or occasional spark.

Customer Question

i have 6hp johnson model j6rcrm with weak or occasional spark. pulled flywheel off found no points nor condensers. slight coating of grease on inside of flywheel. what type of engine do I have, what do I do about the spark?
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Submitted: 4 months ago.
Category: Boat
Expert:  Tan replied 4 months ago.

Hello. My name is Tan.

Have have a 1984 6 hp with capacitor discharge ignition. This is fully electronic ignition. The chances are with an intermittent misfire you have a failing ignition coil. To find the issue you will have to run the engine with the use of a timing light check the spark. Connect the timing light to # ***** spark plug wire run the engine watch the flash of the timing light. You should have a steady flash with no dead spots. If no misfire put light on the bottom plug wire run engine. If you find a misfire on either cylinder swap that coil to the other cylinder. If the misfire moves then that coil is bad. If the misfire stays we have another ignition component failing. This will require the use of a peak reading volt meter or DVA adapter to find the issue.

Post back with questions and findings.

Customer: replied 4 months ago.
when does start it will only run for few seconds on full choke & rich mixture
Expert:  Tan replied 4 months ago.

Try running the engine on a different fuel tank. Full choke and full rich is fuel starvation. So either the fuel pump is failing or you have a fuel restriction. The fuel pump won't come and go so that leaves a fuel supply issue.

Customer: replied 4 months ago.
spark plug got wet with fuel. it just won't start weak or occasional spark.
Expert:  Tan replied 4 months ago.

The plug will get wet with the choke on and full rich. Weak spark can be stator, ignition coil or power pack. We have to do a voltage out put test to determine if the stator is the problem. Then on the ignition coils you have to do the test I posted in the beginning. If both check good then you have a bad power pack.

This statement here tells me you have a dirty carburetor or fuel starvation. "when does start it will only run for few seconds on full choke & rich mixture"

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