Change spark plug wires?

[ultrasport]

Yesterday while troubleshooting and cleaning carbs was isolating a cylinder by pulling plug wire off spark plug to hear engine response. When doing this I noticed that wire when off plug would arc n ground out to nearest bolt and I got shocked once. This happened on 2 seperate wires. I didnt try all 6. I don't believe this is normal as should be better insulated. Should I change wires? Can I just change wire or do have to change wire and coil packs? Suggestions.

 

[Bryan 2530]

Where is the arc coming from??

If from the boot, that is normal, the wire is supposed to carry current to the plug, when you disconnect it, it is going to arc to the nearest ground.

One low budget thing you can do to check wires is run the engine at night and check for arching.

Very rarely to wires go bad on an outboard, temps are to low and the run is too short, unless there is visible damage, leave them be.

What problem are you trying to solve?

 

[DaleH]

Sounds very normal to me too. Remember you are handling HIGH voltage, which by the way, means one typically uses a plastic plug boot removal tool, $5, to do this.

 

[warthog5]

The 90deg boots fail all the time according to my mechanic. Ohm checking the boots on the '95 250 2 Stroke we had showed 3 of the 6 had a "Open" in them.

 

[TomS]

I've had similar experience with plug boots failing on 2 or 3 cylinders. Simple resistance check to test and easy enough to replace.

In my case it helped smooth out a rough low-idling condition.

-- Tom

 

[ultrasport]

Thanks I will def just check resistance. Before replacing anything. How do I check resistance exactly? What type of readings should I be looking for?

 

[johnsw]

As per your other post regarding poor running, if the spark was from the wire for the plug that had the miss then your electricals are fine and would be looking at a combustion problem. But then you already figured that out since your other post also indicated you found a clogged carb jet.

Arc from the wire thats been pulled from the plug is 'normal'. Figure arc over voltage of air is roughly 25KV per inch and the path of least resistance spark plug has been removed, so sounds like your electricals are in good shape. Spark plug voltage can be up in the 30 - 40KV range but low current. Still bites pretty good when it gets ya.

As Dale pointed out, there are insulated boot pullers made for doing this kind of thing. There are also spark testers available (or simple enough to make your own) that plug into the wire boot and more safely indicate if the HV is working. The right tool for the right job.

To check wire resistance, you'll need an ohmmeter. Not sure what the proper resistance, if any, of these wires would be.

 

[DaleH]

As Dale pointed out, there are insulated boot pullers made for doing this kind of thing. There are also spark testers available (or simple enough to make your own) that plug into the wire boot and more safely indicate if the HV is working. The right tool for the right job.

Just note that a spark tester per se won't tell you everything you need to know about a cylinder's performance either. I’ll first use an in-line spark tester (in dim light) as shown below ($6 from Haba Freight or such) to verify that each cylinder is getting spark.

And then if one doesn't have a compression test gauge, I’ll use those insulated plug boot pullers to pull one plug wire at a time off the powerhead. If the RPMs don’t drop when that cylinder's plug is pulled off … then you know you have a serious issues with compression on that cylinder.

 

[ultrasport]

Thanks for info yes boat seems fine now after I cleaned carb found clogged jet which was my problem. I had done compression 95 to 100 in each cylinder. And now I feel comfortable about seeing the arc which dale says is normal.