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Cylinder Checks......


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Hey raiders, wondering if any one could help me sort out something that’s got me buggerd!!!

When I disconnect the top spark plug lead from the actual spark plug while the motor running shouldn’t the motor start to underpreform..Or at least start to choke...

It seems like when I do it has no effect on the outboard. Seem's strange?

When I preform the same with the middle plug lead it has an effect and the outboard and starts to choke.

When the bottom plug lead is removed the engine idles a bit then turns off...

I did the compression check and all seems well at 145psi each.

Can I continue driving this outboard...?

Make: 70 HP Johnson 1998 3 cylinder....

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I would be throwing a set of plugs in,also check and make sure that there is spark at the plug,remove plug,put plug in end of lead,hold with insulated pliers with metal thread of plug on an earth such as cylinder block,crank engine and see if there is spark.maybe a bad coil or plug,eliminate the first things first.may even be a fuel issue.is spark plug black and or wet to indicate a spark issue?if it is dry then I would suggest a fuel issue.

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Hi, if by removing the top high tension lead the outboard does not change its running then the top cylinder is not doing anything. Do a spark gap test and make sure you have three sparks. Then you can swap the plugs and see if the problem follows the plug (or better yet new correct plugs). If still no luck and your compression numbers are fine, you are not getting fuel to that cyclinder. Any engine needs spark, fuel and compression to run and then fine adjustments make it run well.



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Hey thank's for the info guys,

I did the spark plug test and all plugs sparked up fine....

Strangley enough i did another Compression test..This time the top was 146psi the middle was 128psi and the bottom was 145psi....

What do i have to do to get them at the same level psi again....



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