70s 40hp Merc dies after 30 mins of running

recon566

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Sep 1, 2013
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70s 40hp thunderbolt merc. 402 serial number 3408200

Motor starts runs and idles fine. We drive it for a half hour then it dies like you shut the key off. No spark and wont run. Come back the next day and it starts right up and works fine.

Also are the thunderbolt ignition unit compatible with other hp models and years? could I take a 60s 50 hp and try it on my 40 hp 70s?
 
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