1978 Evinrude 85 running rough

[nonstickseven]

I've got a 78' evinrude 85, model 85899C. Runs rough at all rpm's, sometimes there's a POP and a cloud of smoke at idle. New fuel pump, carbs have been rebuilt, new coil packs and plug wires, and plugs. 115-120 on each cylinder on the compression test when hot. When I pull the plug wire off the top left (#2 cylinder i believe?) when looking at the back of the motor, it runs exactly the same as with it connected to the plug. When I pull the bottom left plug wire off, it runs real bad and will die after a few seconds.

I've read in other posts that when you pull one plug wire and it dies, it indicates the opposite cylinder is the problem. I don't fully understand that, feel free to educate me. On that note, I've noticed that when snapping the throttle up from idle the lower port side cylinder doesn't seem to be getting as much fuel dumped into the intake - this is just a visual observation. I still don't understand why the engine runs the same regardless if the top port plug wire is connected or not. Not quite sure if this is a spark/timing or a fuel issue yet. Any help is greatly appreciated.

 

[Boobie]

Check the spark on all four cylinders. Spark should jump a 7/16" open air gap on a spark tester.

 

[MNvoyageur]

When you pulled the plugs, were they all the same color? If 3 are brown and 1 is black, that shows where you issue is. My guess is that your POP and smoke is unburnt fuel combusting in the hot exhaust manifold. This sounds like ignition issues to me- the top left cylinder is probably not getting spark. Was this plug wet/oily?

I wouldn't imagine this is a fuel issue since it's a single carb engine. If 3 of the cylinders are running OK (again, read the plugs), then they should all be getting the right fuel.

The 'opposite plug' idea is more for 2 cylinders. If one cylinder is firing and the other is not, when you pull the plug on the cylinder that is properly firing, the engine dies. Hence, there is a problem with the opposite cylinder.

 

[racerone]

???---MNvoyaguer--------Sorry mate this is a motor with 2 carburetors and 2 barrels each.----Each barrel feeds one cylinder.----So why would it not be a fuel problem with a carburetor?------It might also be a problem with a ruptured diaphragm in the fuel pump ?-----nonstickseven----Does the primer bulb go hard when you operate it ??

 

[nonstickseven]

All 4 cylinders jump a 7/16 gap with the spark tester. The primer bulb does not get very hard after multiple squeezes, I can still touch both sides of the bulb together with two fingers. Would that indicate a bad primer bulb/fuel line or something in the carb? There's occasionally a tiny amount of fuel leaking on the output side of the bulb when squeezing. When I Squeeze and hold the bulb, I can hear air bubbles in the fuel tank. Is that normal? Regardless, I'll pick up a new bulb/fuel line today.