1979 Johnson 70 hp cuts out when quickly opening throttle

Hi everyone, I hope someone on here will be able to help me out.

I've recently bought a boat with above outboard and took it out on Loch Lomond, Scotland a few days ago.
It went ok for about an hour and then all of a sudden cut out as if it ran out of fuel.
It started right back up, but kept dying when I put it in gear.
On land, in neutral and in gear, it will rev up fine if you gradually open the throttle. when you quickly open the throttle it dies too.

Today I have fitted, new fuel lines, new fuel line with primer bulb, new spark plugs, new fuel pump and stripped and cleaned all 3 carburettors (I didn't remove the high speed jets, but sprayed carb cleaner and used compressed air to blow them through). Done a compression test 125, 125, 130.



I have run out of options.
Anyone any idea what I can check next?

Does spark jump a gap of 7/16" on the 3 leads, yes or no ?----And when it is " on land " and you rev it up in gear it really is still in nuetral.----------The prop does not do any " work " moving just air.

racerone said:

Does spark jump a gap of 7/16" on the 3 leads, yes or no ?----And when it is " on land " and you rev it up in gear it really is still in nuetral.----------The prop does not do any " work " moving just air.

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I was only trying to point out that it will also stall on land, not just under load.
Umm 7/16"? What is that in mm?

10 mm or there abouts

racerone said:

10 mm or there abouts

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Thanks.
How do I test if it jumps 10mm? Hold the spark plug 10mm away from the head?

Stick a phillips screw driver in the end of the plug wire and hold that 7/16 " away from the block or a good ground. It sounds like you still have some carb probs though.

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