weak spark ???

[piggy]

10 H. P. Johnson Q D 15 had no spark. Put new condensers, points (set to .020) had coils checked by dealer was o. k. Get spark on both plugs but only will jump gap on spark tester set at about .060. motor will not start. Is this spark o k ? If not what is wrong? It poped once. Could coils be weak but still test o k. Thanks for any help.

 

[piggy]

weak spark Johnson 10 h.p.

weak spark Johnson 10 h.p.

10 H. P. Johnson Q D 15 had no spark. Put new condensers, points (set to .020) had coils checked by dealer was o. k. Get spark on both plugs but only will jump gap on spark tester set at about .060. motor will not start. Is this spark o k ? If not what is wrong? It poped once. Could coils be weak but still test o k. Thanks for any help.

 

[F_R]

Re: weak spark ???

Can coils be weak and still test OK? Absolutely!! Especially if they are old ones. It should jump a 1/4" gap with ease. .060 is nowhere near good enough.

Don't ignore the spark plug wires. Check for continuity all the way from the plug cap back through the coil's secondary winding. They also often arc through where they are clamped up under the plate.

 

[lexkyboater]

Re: weak spark ???

My understanding is that coils go bad over time. Check primary resistance yourself between green and black wires and should be about 1.0 ohms. The secondary resistance between green wire and plug wire stinger should be at least 70,000 ohms. I had old coils on my 71 7.5 HP and they were 78,000 and 80,000 ohms. New OMC coils were 92,800 and 93,800 ohms. I totally agree with F_R on the plug wires - check resistance with a meter and wiggle them to see if there are any open circuits. One of my wires had an open when I wiggled it, which meant it was opening when I advanced the timing as I turned the throttle. Checking with spark tester showed a yellowish spark that only jumped 1/4" and after new coils and plug wires it jumped 5/16" with a nice blue arc. All that said, I agree it's likely plug wires, and we've seen a lot of posts with that problem in the last month. Seems that something that is really overlooked when a major tuneup is done. --Steve

 

[wbeaton]

Re: weak spark Johnson 10 h.p.

Re: weak spark Johnson 10 h.p.

You should have more spark than that. If they are the original coils then they need to be replaced. They are always bad. I've had old coils start and run fine in a barrel, but fail on the boat. Are you still using the original spark plug wires? Maybe the coils were replaced and work fine, but the wires are failing.

 

[wbeaton]

Re: weak spark ???

Double post. I responded to the other before seeing this one. I said exactly what FR did.

 

[samo_ott]

Re: weak spark Johnson 10 h.p.

Re: weak spark Johnson 10 h.p.

I agree, it's usually the coils. But what's the compression, have you checked that yet? It needs compression, fuel and a good spark to run.