50 hp Johnson 1972 weak fire???

[RandyJ]

I finally got around to building a spark checker. Yep, it has nice pretty blue fire but it only jumps about 1/8". I put new plug wires on and that didn't change anything. It cranks good and runs okay but just won't idle at low speed. Carbs have been thoroughly cleaned and checked over again and again. I have to open the throttle just a little past where the little wheel opens on the timing cam to keep it running. Just wondering what other's opinions are. I kind of suspect the coils being the problem. I would not have a clue if power pack would cause this problem or not. I just know that it should idle easier.

 

[RandyJ]

Re: 50 hp Johnson 1972 weak fire???

No takers? Come on guys! I am not too sure how to check the power pack for input or output... so I don't want to just throw parts at this motor. I need at least some informed opinion as to whether or not I should replace the coils on this motor. If I need to replace the coils I need to order them today....

 

[F_R]

Re: 50 hp Johnson 1972 weak fire???

Something sounds fishy here. That motor should jump a 7/16" gap with ease. In fact, it will jump an inch, but don't try it because that's a coil buster.

I don't see how it could run at all with only an eighth of an inch. But I guess you proved it will.

The power pack is probably ok. They usually work or don't work. How are your charge coils (the two big ones under the flywheel)? Are they melted?

Without proper test instruments, the coil queston is a guess at best.

EDIT: Forgot to mention what should always be the first troubleshooting step---disconnect the black/yellow stripe wire from the power pack and try it again. It could be bleeding off some of the energy and not fully charging the capacitor in the power pack.

 

[RandyJ]

Re: 50 hp Johnson 1972 weak fire???

Thanks... I haven't pulled the flywheel so I'll do that to take a look at them. This old motor set up a few years before I got it... I had it running about 5 or so years ago then it set up again until now. I've never had it in the water...

 

[RandyJ]

Re: 50 hp Johnson 1972 weak fire???

Stator is putting out over 15 volts ac. Timer base coils check out okay according to the directions in the CDI trouble shooting guide. Still weak spark. Checking kill circuit next....

hmmm... might be right! I bought one of those fancy spark checkers from CDI... after pulling the black/yellow kill wire going to the harness I'm getting 1/2" spark on both plug wires! I guess next thing I'll do is put some gas to it and see how it runs.... and I'll ohm the kill wire for shorts.

Yep... got some ohms from the kill wire. Starts above 10 Mohms then bleeds down and starts all over. I'd bet that old control box is full of mud dauber homes among other possibilities. It has kick butt fire now! I'll get gas on it soon and see how it runs.

 

[AlTn]

Re: 50 hp Johnson 1972 weak fire???

thanks for posting back with results...be careful if you begin testing w/o a kill circuit

 

[RandyJ]

Re: 50 hp Johnson 1972 weak fire???

thanks.... got that covered. Safety is HUGE with me...

 

[Hoyt79]

Re: 50 hp Johnson 1972 weak fire???

Bringing this old thread back up, because I am sort of having the same issues with the very same motor...my spark is a little weak too. Whats this I hear about a black/yellow kill wire to disconnect from the power pack?

 

[BonairII]

Re: 50 hp Johnson 1972 weak fire???

Bringing this old thread back up, because I am sort of having the same issues with the very same motor...my spark is a little weak too. Whats this I hear about a black/yellow kill wire to disconnect from the power pack?

Probably best to start a new thread on the subject.

 

[RandyJ]

Re: 50 hp Johnson 1972 weak fire???

Probably best to start a new thread on the subject.

Maybe/maybe not. It's still sitting at the front door of my house and I haven't had time lately to mess with it. Maybe I'll find someone who needs a nice little project bass boat and will take it off of my hands!!!!! Not like I don't have enough projects without this one....