Motor running goofy

[iggyw1]

I have a 1984 Johnson outboard motor, 70 H.P. That runs perfect at low speeds. Every once in a while, at WOT, it seems like I lose one cylinder completely as the motors keeps running but bogs down slower for a few seconds (like 6-7 seconds) then seems like the cylinder kicks back in and runs fine at WOT. After a few minutes of running WOT, it will do the same thing again, bog down like it lost a cylinder, then all of a sudden after a few seconds, will pick up all cylinders again. It does not happen all of the time, but every now and then this happens. What should I look at?

 

[interalian]

I'd start by having somebody squeeze the primer bulb when it's misbehaving at WOT. If that helps, you have a fuel issue. If it doesn't help, hang a timing light on each spark plug in sequence and see if you're losing spark.

 

[Silvertip]

Portable fuel tank or built-in? When the problem appears, look at the primer bulb. If it is being sucked flat there is a restriction in the fuel line between the bulb and the pick up in the tank. If not, then the fuel pump/fuel filter/spark plugs/carburetors are suspect. Check the cheap stuff first.

 

[emdsapmgr]

Heat is the enemy of ignition components of your engine. When some of these components get old and the engine warms up, the component may not work perfectly. Ignition problems usually are of the type that the component works or does not work. That sounds like what you are experiencing. Check for spark when the engine starts to bog. It may only be running on 2 cyls. Weak components may work fine when the engine just starts and is not completely warmed up. When the engine finally reaches normal operating temps, a component may become erratic.