Firing on one cylinder....Coils or power pack?

[sth5591]

I have been chasing issues on my '79 70hp Johnson for a year now. I started with a fuel pump rebuild, then a new fuel line and primer bulb, rebuild of all 3 carbs. Still doing the same thing. Seems to start up and idle alright, when you throttle up it bogs down and the boat will top out at 6 knots. In testing the spark on muffs today I can pull the plug wires off the center and bottom cylinders and that will make no difference in how its running. When I pull the top plug wire the boat will die. So to me this means the bottom 2 cylinders are not getting spark, or at least very weak spark. Do I start with coils or power pack? Also when unplugging the plug wires I was getting small zapped from the bottom two cylinders, but not the top. Connectors and the nut at the terminal on the coil are also quite corroded, moreso on the lower 2 cylinders.

 

[flyingscott]

Clean all the terminals to shiny and retry. If that makes no difference move the coil from the good cylinder to one of the bad ones and see if you get spark. If you don't it is probably the powerpak go to www.cdielectronics.com for the testing procedures for the powerpak.

 

[sth5591]

Thank you, I didn't realize the terminals were corroded until just now. When testing spark by touching the plug to the block I'm getting spark on all 3, but I don't have a real spark tester. A local boat mechanic told me the power packs often won't act up until the engine is put under load, which would describe my issue.

 

[clemsonfor]

A power pack that's gone out is done sometimes. That's how my 81 johnson 2 cyl went. Just lost it if I remember er right....wait mine was the stator.

CDI has tests on their site to preform to narrow it down.

 

[racerone]

Have you done a compression test ?------How about spraying some mixed fuel into the bottom 2 cylinders while it is running.---Some simple testing can save you a bunch of $$$ and a lot of grief.

 

[sth5591]

Looked a bit closer at the bottom coil, it looks like it had cracked at some point and been glued back together, and was starting to come apart again. Had another issure I found with the throttle not opening 100% without really forcing the arm, but that doesn't solve the misfire.

 

[flyingscott]

If the motor is not running DO NOT force the throttle. Have somebody manually turning the prop then shift into gear and you will get full throttle. Replace the glued coil regardless. Only turn the prop if the motor is not running.

 

[Newyota]

Looked a bit closer at the bottom coil, it looks like it had cracked at some point and been glued back together, and was starting to come apart again. Had another issure I found with the throttle not opening 100% without really forcing the arm, but that doesn't solve the misfire.

Did you clean any ground wire connections?

 

[boobie]

Go to cdielectronics.com for ignition trouble shooting.

 

[CaptnKingfisher]

Sounds like its no longer a spark issue.. but if you ever suspect a coil in the future for a no spark issue theres an easy way to verify/eliminate that.
Example: No Spark on No. 1 plug, but #2 plug sparks perfectly.
Remove the plug boots from the plugs so engine can't start.
Open powerpack and switch coil 1 wire with coil 2 wire on the powerpack terminals
Retest your previously not firing coil. If it fires now then you can rule out the coil being bad and the problem is now in or before the powerpack.

If you need me to clarify I can. Easier to show these things than to explain in words !

 

[sth5591]

After replacing the coil the bottom cylinder is still not firing. However, I realized I did not have gas spraying out of the carb, but water. So I'm thinking the water jacket cover gasket needs to be replaced....

 

[oldboat1]

not if water is coming from the carb, though? That would be an issue with the fuel supply.

 

[sth5591]

not if water is coming from the carb, though? That would be an issue with the fuel supply.

The spark plug looks milky too. I switched the carb and coil from the top cylinder to the bottom and it sprayed water then too, and the top cylinder fired fine with the carb from the bottom cylinder. I've narrowed it down to water jacket gasket, head gasket, or exhaust gaskets.

 

[Tim Frank]

I have been chasing issues on my '79 70hp Johnson for a year now. I started with a fuel pump rebuild, then a new fuel line and primer bulb, rebuild of all 3 carbs. Still doing the same thing. Seems to start up and idle alright, when you throttle up it bogs down and the boat will top out at 6 knots. In testing the spark on muffs today I can pull the plug wires off the center and bottom cylinders and that will make no difference in how its running. When I pull the top plug wire the boat will die. So to me this means the bottom 2 cylinders are not getting spark, or at least very weak spark. Do I start with coils or power pack? Also when unplugging the plug wires I was getting small zapped from the bottom two cylinders, but not the top. Connectors and the nut at the terminal on the coil are also quite corroded, moreso on the lower 2 cylinders.

Looks like you are all over the place with no method to your efforts. You need to be systematic in your troubleshooting or you just end up throwing parts at the problem without a really rational reason or much likelihood of success....although they say even a blind squirrel sometimes finds a nut.

You need to check spark with a proper tester....should jump a 7/16" gap. If it does that you have pretty much verified your ignition system with a 10 minute test using a LT $10- tool....you probably paid more than that for the fuel system parts that may not have been needed Grounding the plugs on the block tells you little or nothing.
Then check compression with a proper gauge. With your description of events I'd expect readings of something like 100-0-0....at least on that order.

Have you done a compression test ?------How about spraying some mixed fuel into the bottom 2 cylinders while it is running.---Some simple testing can save you a bunch of $$$ and a lot of grief.

That was post #5....nothing suggests that you even read it. This guy really knows his stuff, if you are fortunate enough to get him involved with an OMC problem, your chance of success is greatly increased. JMHO.