Spark problems on a Johnson 90 hp 1985 (Model: J90TLCOS)

[steinn39]

Hi I just bought an old boat whit a Johnson 90 hp 1985 (Model: J90TLCOS) outboard motor on it. The motor had not been run for a few years. After cleaning out the carb and replacing the water pump I tried to get it running. But it would not start. I did a compressor test and all the cylinders where fine. I am getting fuel. But a weird think is happening with the sparkplug.

So here is my problem.

If I have no sparkplug in the cylinder I get a spark but as soon as the sparkplug is screwed in there is no spark on that cylinder. For example I remove all the sparkplugs and I get sparks on all 4 ignition cols , then I screw in the spark plug for cylinder 1 and I only get sparks on ignition cols 2,3,and 4.

Does any one have any idea what is going on?

Best regards

Steinn

 

[jonesg]

Re: Spark problems on a Johnson 90 hp 1985 (Model: J90TLCOS)

You can't do a spark test with a sparkplug.
Using a spark tester would show it fails the test. You have weak spark.
Try unplugging the powerpack and spray clean the plug and terminals with elec cleaner (CRC from NAPA).
I would go over all the terminals to eliminate that from the problem.
Clean coil grounds. Check coils for cracks.

 

[steinn39]

Re: Spark problems on a Johnson 90 hp 1985 (Model: J90TLCOS)

ok thanks
but what is the cap I should use on the spark tester. 1/4?

 

[emdsapmgr]

Re: Spark problems on a Johnson 90 hp 1985 (Model: J90TLCOS)

The spark from that ignition system should jump a 1/2" gap.

 

[steinn39]

Re: Spark problems on a Johnson 90 hp 1985 (Model: J90TLCOS)

So I got my self a spark tester and, there was no spark a ? inch but I got a spark on ? inch on 3 sparkplugs. So I did an Ignition coil resistance test and the manual sad it should be 225-325 ohms
Cylinder1, 22 ohms
Cylinder2, 266 ohms
Cylinder3, 266 ohms
cylinder4, 262 ohms

So I have a couple of questions

1. Can I replace just one ignition coil or should I replace them all?
2. Is this the reason there is no spark at ? inch?
3. Where can I get the ignition coil?

Hope you can help me
Best regards Steinn

 

[SparkieBoat]

Re: Spark problems on a Johnson 90 hp 1985 (Model: J90TLCOS)

yes you can replace just one coil..but clean the ground first then recheck spark,