70hp Evinrude with weak spark

[AC156]

I recently bought a boat that has a 1975 70 hp evinrude, model number 70573E. I got the engine running and it idled good for about 5 mins. Since then I haven't been able to get it started. The bottom cylinder is firing, the middle cylinder has a very weak spark, and the top cylinder is not firing at all. I have tried new plugs with no luck. Does anyone have an ideas about what is causing this?

 

[a70eliminator]

Re: 70hp Evinrude with weak spark

dual point ignition w/dual condensers? Is all that set up with proper gaps?

 

[AC156]

Re: 70hp Evinrude with weak spark

We got the engine to start again last night. It ran good for about 5 mins, then died. We took it out of the water and hooked a timing light up to it to see if it was getting fire. The bottom cylinder was the only one firing. Any more ideas?

 

[tlynch99]

Re: 70hp Evinrude with weak spark

I have a question, I have a similar vintage evinrude. Do you think that only one of the cylinders was firing when you had it in the water? Did it sound like it was running smooth when only the one was firing? Mine misses every so often when idling and I wondering if I should start with the electrical system or rebuild the carbs...?

Thanks,

 

[AC156]

Re: 70hp Evinrude with weak spark

I just went out and took the wire going into the bottom coil off and hooked the middle coil up to that spot. The middle cylinder had fire when I did that. I then put the wire going into the top coil into the bottom spot and that coil fired. Since I am getting fire out of the coils when I swap the input wires, I would think that the coils are good. What else do I need to check?


tlynch99, when I had it running in the water, I'm pretty sure that it was running on more than one cylinder. It sounded pretty smooth when it was running, like the other two cylinders started firing.

 

[AC156]

Re: 70hp Evinrude with weak spark

Could one cylinder still be firing if the powerpack is bad, or would all 3 cylinders be dead?

 

[willamettejeff]

Re: 70hp Evinrude with weak spark

Since coils seem to be ok, suggest you try swapping timing sensor wires next. They are the ones on the upper right on the power pack labeled 1, 2 and 3. The bottom cylinder is #3. This will tell you whether it is the power pack or the timing sensor and yes, you can have a partially dead power pack. Since one cylinder is firing, probably not the stator, but not to say it couldn't be. Suggest you get a manual for your motor. It will have the procedures for troubleshooting the ignition components. At the cost of parts, manual is cheap. BTW, I have a 1978 70hp Johnson on my boat.

FYI, A70, no points and condensers after 1969 on the J/E 70's.

 

[AC156]

Re: 70hp Evinrude with weak spark

I swapped the sensor wires going into the power pack and had the same symptoms. The bottom cylinder had fire and the other two did not. That tells me that there is fire coming from the sensor wires but not through the power pack on the top two cylinders. I then pulled the power pack and checked it with an ohm meter. There showed to be a connection between the two leads on the third cylinder and the top two cylinders showed an open circuit. So I guess I have a bad power pack. Am I correct in thinking this?

 

[willamettejeff]

Re: 70hp Evinrude with weak spark

Looks to be a dead powerpack. Suggest before running after replacing that you check the resistance on all three coils to make sure they are the same as the one on cylinder 3. Also check leads to coils for any breaks in the insulation. Bottom cylinder firing with any of the 3 sensor wires suggests your stator is good as well as your timing sensor. Be sure to clean all coil ground wire terminals and all other terminals connected to power pack. Also, check for any voltage on the black/yellow wire connected to lower left terminal on the powerpack for any voltage to ground with ignition key in either the off or on position. Do this with the wire disconnected. This wire gets grounded when the ignition is turned off to turn off the motor. Any voltage on this wire can fry the power pack.

 

[AC156]

Re: 70hp Evinrude with weak spark

The new power pack came in today. The engine runs like a top now. Thanks.