1978 70hp johnson runs then stops!

atlapp

Seaman
Joined
Sep 25, 2010
Messages
51
Bought a new project boat, LOL, Yet another money pit! Motor Fires right up runs for 15 to 30 seconds like a top, then dies and will not restart until it cools down. Just rebuilt all carbs, I am convinced it is not a fuel issue...tryed many of the test procedures I found on this great website....removing rectifer wires...stator wires etc... with no luck...clearly this is a power pack, stator or trigger problem....I am leaning towards power pack...any ideas on how to narrow this down...spark does appear to be a little weak and get no spark after it is warm...thanks in advance for any help you can give a dumb real estate appraiser trying to be and outboard mech...LOL...most of contunity test I did checked out ok, however voltage between 2 stator wires at power pack was only around 50v...not sure if that helps or not!
 

Larry69

Recruit
Joined
Jul 16, 2011
Messages
3
Re: 1978 70hp johnson runs then stops!

Does it bog a little before it quits???

A Vac. leak in one of the cyls. could cause a serious lean issue... boiling the fuel before it fires ......spray around w/ carb clean and listen for the rpms to change...and are you hearing any pinging ( I know they are loud ) but thats a dead give away for pre detination..........
 

Daviet

Fleet Admiral
Joined
Sep 24, 2008
Messages
8,958
Re: 1978 70hp johnson runs then stops!

You need a factory manual, it has all the specs and test procedures to help you find your problem.
 

atlapp

Seaman
Joined
Sep 25, 2010
Messages
51
Re: 1978 70hp johnson runs then stops!

Any suggestion on what manual...or does it matter? I am not hearing any pinging, againg pretty sure this is not a fuel issue!
 
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