1974 Mercury 7.5 Outboard- No Spark

walter227

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Hello all, I have a 1974 Mercury Outboard 7.5 hp serial number 7029200 . Ran good 2 years ago , now there is no spark. I tested the coils for continuity between the positive and negative terminals of each , and they tested ok. Pulled the flywheel , everything looks in order. When turning the tiller and advancing the throttle,there are 2 metal bands that make contact to advance or retard the timing . There is no reading from the ohm meter to the two brown wires that feed and connect via a bus running to the switchbox when advancing or retreating the throttle. Could one of the metal contacts not contacting cause a no spark condition?

I have cleaned all connections including the spark plug wires where they plug into the coils, cleaned the coils, where the spark plug wires plug into and bypassed the kill switch to both open and ground, and still no spark.

Any ideas greatly appreciated , need my kicker soon!

Thanks, Walt :joyous:
 

walter227

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Re: 1974 Mercury 7.5 Outboard- No Spark

Hi,I have pulled the flywheel and I don`t see any points,the only wires coming from that area are 2 brown wires coming from the magneto that attach via a bus to feed the switch box. I dated the motor by the serial number..it has the Thunderbolt Ignition system . Will the attached diagram still help?

Thanks, Walt
 

Laddies

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Re: 1974 Mercury 7.5 Outboard- No Spark

No, it won't work if your engine does not have points then let me have the number off the switch box, your right it is a 74 and that should be the right test but it is apparently not, with the switch box number we can get the right one.
 

walter227

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Re: 1974 Mercury 7.5 Outboard- No Spark

Cannot locate a p/n on the switchbox, shall i remove it for a thorough inspection? Thank you so much for thr help this far ..Walt :)
 

walter227

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Re: 1974 Mercury 7.5 Outboard- No Spark

Yes it does, exactly! My coil for the lower cylinder has a green / white stripe wire to the negative, and light green to the positive; the upper cylinder has a black or brown wire to the positive, and a green / white stripe to the negative. IMG_20130417_182954.jpg The throttle advance, I get no reading when testing the bare metal strips to the brown wires, is this a problem?:confused: The top plate does not touch the stator housing IMG_20130417_184056.jpgPlease post test instructions if possible and thank you kindly for your help

~Walt :)

EDIT: I found so far that the stator may have been changed- the throttle advance was not making contact with it , there was paint preventing that. i sanded it clean and adjusted the tab to make full contact and now get a reading. Also found the two brown wires go inside a rubber housing and the tab slides in and out freely, I am assuming communicating with the throttle advance and the flywheel is that correct? Thanks again,
 

Laddies

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Re: 1974 Mercury 7.5 Outboard- No Spark

Walt sorry about the confusion here's the right test
 

walter227

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Re: 1974 Mercury 7.5 Outboard- No Spark

Thanks so much! What I have found, is the lower cylinder coil the positive and negative both show ground to the engine, the upper cylinder coil shows no ground on either the positive or negative.. are the wires on the wrong sides? Right now I have both the green/white wires on negative each side,the top cylinder coil has a brown or black to the positive,and the lower cylinder coil has a solid green to the positive....
 

walter227

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Feb 9, 2012
Messages
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Re: 1974 Mercury 7.5 Outboard- No Spark

Thanks so much! What I have found, is the lower cylinder coil the positive and negative both show ground to the engine, the upper cylinder coil shows no ground on either the positive or negative.. are the wires on the wrong sides? Right now I have both the green/white wires on negative each side,the top cylinder coil has a brown or black to the positive,and the lower cylinder coil has a solid green to the positive....

Coils check ok , stator checks ok, throttle advance is making contact, no readings from either the positive or negative terminals of both coils when touched to engine ground, bypassed the kill switch to ground,cleaned backside of both coil wires and the ground on the engine they touch on, on the stator can the coils read through the painted armature?I think someone may have messed with the wiring to the coils. What is the proper combination, do they criss cross ? On the lower cylinder coil I have a green/white and a black or brown, on the upper cylinder coil I have a Green/white and a solid green. Both green / white are to the negative side of the coil, the brown/black to positive, and the solid green to the positive. Is this correct? Thanks,
 
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