71 johnson 100 hp power loss weak spark on throttle advance

[edub512]

Need some help here boat starts and idles perfect i can even throttle up a little bit but when i get to about 1/3 throttle the boat begins to choke out and alot of smoke starts coming out of the exhaust. I checked the spark plug wires with an open air tester and while doing this on all 4 cylinders when i begin to throttle up spark dies out or becomes very weak. Can any one help me solve this problem. From what i have read it could be a faulty power pack or coil i have a DVA can anyone tell me how to test either or both of these when it begins to bog down.

 

[Faztbullet]

Re: 71 johnson 100 hp power loss weak spark on throttle advance

Here is factory troubleshooting chart...

View attachment IMG.pdf

 

[edub512]

Re: 71 johnson 100 hp power loss weak spark on throttle advance

Thanks i'll do some tests when i get home. What manual is this from i have a service manual for my boat but the info in my manual is vague when it comes to trouble shooting.

 

[rockyrude]

Re: 71 johnson 100 hp power loss weak spark on throttle advance

Check the two wires that go from the power pack up along the timing arm and then under the flywheel. There is an anchor clamp just before they go under the flywheel. On mine the insulation on the wires cracked and when the timing arm moved the wires shorted to the clamp, killing the sensor signal to the power pack.

 

[edub512]

Re: 71 johnson 100 hp power loss weak spark on throttle advance

Thanks I'll check that also I had to cut and splice all the wires that were connecting to the power pack because they were so old and deteriorated. One goes to ground and the other to the power pack.

 

[Faztbullet]

Re: 71 johnson 100 hp power loss weak spark on throttle advance

What manual is this from i have a service manual for my boat but the info in my manual is vague

Its from my OMC service training years ago, cant remember if if I got it at Fond Du Lac or Morrow service school....

View attachment IMG.pdf

 

[edub512]

Re: 71 johnson 100 hp power loss weak spark on throttle advance

rockyrude you freakin nailed it where i spliced the wire from before it was actually bare right by were connected to the points. thank you guys so much for the advice. Gonna be boating tomorrow hopefully if i get off work early enough.