1991 Force 120 idling rough, missing and 1 spark plug black

[cobia17]

The motor has new plugs, timing just done, fuel recirculation screens cleaned and good gas. Runs rough, especially in idle and sounds like it's missing. 1,3 and 4 cyl. Plugs are wet and no black residue. 2nd cyl. Has black soot residue. Can anyone tell me what this means?

 

[Jiggz]

You seem to have water intrusion in all three cylinders with those very clean and wet spark plugs. With such degree of intrusion it is most likely coming from the exhaust manifold. The #2 spark plugs indicate a very rich fuel oil mixture which means the air-fuel oil screw is not set correctly. It should be 1 1/8~1 1/4 turn out from slightly seated or you have improper fuel oil mix which should be 50:1. Since #1 and #2 cylinder shares the same carb, I would expect #1 plug to be carboned up too unless it is being steam cleaned with that water intrusion.

Removing the exhaust plate is a very challenging proposition due to the fact the small bolts have a tendency to snap rather than break lose. If you can ascertain there is water intrusion, the next step is to remove the exhaust manifold.

 

[cobia17]

Thanks, the wet plugs are wet with fuel not water. I'm running it at 25:1 not 50:1 just because it was a new engine to me. Are the plugs wet with fuel normal? And is the carboned up black plug normal just rich?

 

[cobia17]

Jiggz, the air-oil screw is at 1 1/4 turn.

 

[Jiggz]

OK, that means there is misfiring/non-firing if fuel wet and not water wet. Is the engine new/newly rebuilt or just new to you. If it is the latter the mix should be 50:1. And yes, it is normal for plugs to be a little wet or even dry but not dripping wet and also there should be some trace of carbon but not totally covering the surface of the plug. Normally, there will be some browning on the surface with a little carbon and almost dry if firing correctly.

 

[Jiggz]

To check for misfiring get an inline spark tester from auto stores appox $10 and check to make sure you have spark on all cylinders. If all cylinders have spark then you need to check for misfiring by pulling each plug wire off (quickly to avoid CD damage) while listening in changes in engine rpm. If there is change it means that cylinder is firing. If there is no change it means that cylinder is not firing. do a compression test first to make sure it is not worn out rings. From there you need to start troubleshooting on what is causing non-firing.

 

[cobia17]

Thanks jiggz, I started pulling plug wires and when I got to cyl 2 it shocked me. The others didn't shock me. It shocks me hard enough that I cant remove the wire. The other 3 wires made a big difference when I removed them. I also checked the spark on all 4 and all are firing. What could make cyl. 2 wire shock me? I will do compression check tomorrow?

 

[Jiggz]

Electrical shock from plug wires is caused by old worn out rubber boot where the dielectric property of the rubber has deteriorated really bad. The problem, unlike the old style plug wires, these wires are permanently attached to the CD modules but you can still replace the boot portion if you wanted to. Or just like in my case, you can just use dielectric grease between the plug's tips and the rubber boot. Contrary to its name dielectric grease maintains good conductivity between mating surfaces and protects them from dirt at the same time. If you google, there is step by step procedure on how to do compression tests under Utube.

 

[cobia17]

Jiggz, thanks for your time and expertise! Compression test next.