1973 Merc 150 no spark after half throttle

[Clarky_kris]

It will start and idle then when I give it some throttle spark cuts out engine sputters and sometimes starts running backwards... I put new plugs in it and same thing... I checked spark while engine running and soon as it starts to sputter spark is gone... What can this problem be??? any help to get me back on the water... It was running fine all day on the lake... I started engine to go back to dock and it just hit all of a sudden... Bearly made it home.. Plz help
1973 mercury 1500 thunderbolt i6

 

[Clarky_kris]

Re: 1973 Merc 150 no spark after half throttle

Ok I just did the "MERCURY BATTERY-POWERED CDI TEST FOR DISTRIBUTOR MODELS" and results were I had no spark when grounding black wire to switchbox.. Cleaned all conections and 12v power is where it should be... From results of this test tells us either the switchbox or coil are faulty?? Is this correct?? What should my next steps be? Can I check coil resistance?? And how is it done? Thanks

Kris

 

[Clarky_kris]

Re: 1973 Merc 150 no spark after half throttle

Tttt. Please help!!