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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11076
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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NO SPARK AT TIMES OTHER TIMES IT WILL START, AT TIMES I HAVE

This answer was rated:

NO SPARK AT TIMES OTHER TIMES IT WILL START
JA: Sometimes things that you think will be really complicated end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so the Marine Mechanic can help you best.
Customer: AT TIMES I HAVE GREAT SPARK TO PLUGS AND IT FIRES RIGHT UP THEN OTHER TIMES I HAVE NONE AT ALL AND CANT GET IT TO COME BACK
JA: Is there anything else the Marine Mechanic should be aware of?
Customer: 1971 JOHNSON 50HP OUTBOARD NEW COILS FULLY CHARGED BATTERY 900 CCA

Hello, I'm Tan. Welcome to JustAnswer. I'm reviewing your question and will reply momentarily.

When you have no spark disconnect the black/yellow wire from the power pack. Does spark return?

Customer: replied 1 month ago.
NO
Customer: replied 1 month ago.
I HAVE ALSO REMOVED WIRES FROM THE RECTIFIER AND TRYED STILL NO SPARK

Being intermittent we will have to check the stator and the timer base outputs with a peak reading volt meter or a DVA adapter for your meter. The rectifier is part of the charging system not ignition.

I will say the most likely cause is the power pack as the stator and timer base are just coils with no electronics to turn on and off. Where as the power pack has circuitry that can cause this issue.

Customer: replied 1 month ago.
IT IS SO STRANGE AT TIMES IT WILL START RIGHT UP AND OTHER TIMES I CAN CRANK IT ALL DAY IF I WANTED AND NO SPARK AT ALL
VERY HIT OR MISS
Customer: replied 1 month ago.
HOW DO I TEST THE POWER PACK AND WHAT SHOULD I GET FOR READINGS DURING THE TEST

There is no test for the power pack we can only test the inputs and we have to do this with a peak reading volt meter. This is a cranking test of the stator and the timer base.

Customer: replied 1 month ago.
HOW DO I DO THIS TEST AND WHAT SHOULD I GET FOR READINGS

Do you have a peak reading volt meter?

Customer: replied 1 month ago.

Disconnect the brown lead coming from the stator, connect the positive lead to the brown and the black lead to engine ground crank engine over. You should have 150-400 peak volts. Then on the timer base disconnect the white/black and black/white from power pack and test between the 2 wires you should have .6+ peak volts when cranking. These test are done cranking the engine when you have no spark.

If these are in spec then the power pack is the problem if out of spec that is the failing component.

Post back with questions and findings.

Customer: replied 1 month ago.
I HAVE A MM700 MULTI METER FROM KLIEN TOOLS WILL THAT WORK
Customer: replied 1 month ago.
Product Features
Automatic ranging true root mean square (TRMS) technology for increased accuracy
Measures up to 1000V AC/DC voltage, 10A AC/DC current and 40MΩ resistance plus temperature, capacitance, frequency, duty-cycle, diodes and continuity
CAT IV 600V Safety Rating
Built to withstand a 6.6' (2m) drop and withstand daily wear and tear on the job site
Low Impedance (LoZ) mode for identifying and eliminating ghost or stray voltages
For use in basic and controlled electromagnetic environments such as residential, business and light-industrial locations
Low battery indicator and easily accessible battery and fuse replacement compartment
Includes carrying pouch, test leads, alligator clips, thermocouple with adapter and batteries
Customer: replied 1 month ago.
IM WAITING FOR THE DVA ADAPTER TO ARRIVE THEN ILL TEST IT

Ok keep me posted.

Customer: replied 1 month ago.
WHAT SPARK PLUG IS BEST FOR MY 1971 JOHNSON 50HP OUTBOARD I CURRENTLY HAVE NGK B7HS PLUGS

The factory spark plug is Champion UL77V this ignition system is designed to use this plug. Now the alternative plugs are listed here. http://www.sparkplug-crossreference.com/convert/CHAMP_PN/UL77V

The plug you are using isn't listed. You must use correct spark plug to get the best performance.

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