The never ending weak spark saga

I'll try to summarize so that as many people read this as possible.

1974 Evinrude 135 HP, Problem-- fouling spark plugs.

We have tried different oils, different ratio's, different spark plugs, rebuild carbs, adjusted floats, checked compression, link & sync, 4 new coils all to no avail. We troll a lot but I still think it is unacceptable to have to buy 4 new plugs every time we go out. CDI trouble shooting guide has been close companion. My stator is oozing goo, but still gives me voltages withing the acceptable range. I already tried a new powerpack, but my spark still seems weak (as seen jumping a 7/16" gap) and is intermittent. (trigger coils are also doing their jobs.) My theory is that even though I have correct voltages going to my power pack my current (amps) might be low which is causing a weak spark and incomplete combustion.

Has anyone ever had such an issue? Now I did break down and buy a new/used stator, but wanted someone to attest to my theory before I started the swap..

I have been told that if the spark jumps the gap that it is strong enough, but I'm not convinced. I want to see a bright fat blue spark and all I'm getting is a skinny faint yellow arc.

Tell me your thoughts, Thanks

Re: The never ending weak spark saga

If your only problem is fouling spark plug(s) and it is happening because you troll a lot with your outboard, you could go to a hotter spark plug and/or lean the carb a little (just a very little) to try and eliminate the fouling. Hotter plugs will maybe burn off the fouling better than regular types... Are all the plugs doing the same thing? If so then your problem/solution is going to be the carb(s) or plug heat range...

Re: The never ending weak spark saga

gm280 said:

If your only problem is fouling spark plug(s) and it is happening because you troll a lot with your outboard, you could go to a hotter spark plug and/or lean the carb a little (just a very little) to try and eliminate the fouling. Hotter plugs will maybe burn off the fouling better than regular types... Are all the plugs doing the same thing? If so then your problem/solution is going to be the carb(s) or plug heat range...

Click to expand...

That isn't the only problem, idleing is an issue too. I have tried hotter plugs, and my carbs are fixed jets, so I can't lean them out. Thanks for the ideas.

Re: The never ending weak spark saga

Okay fixed jets... Well you either still have a carb problem (in the low idle circuit) and if not then you will have to live with it or change to a carb with adjustable either air bleed or gas bleed adjustments... NO other way to fix your trolling plug fouling issue. IMO!

Re: The never ending weak spark saga

The spark plug coils are usually pretty reliable. The power pack statistically is the high failure item. Since it and the stator are both expensive, some troubleshooting will make sure you invest in the correct parts. I'd start with the stator, since you already question it. I check stators by cranking, then checking the voltage output-per the CDI stated voltages. On your engine, you need to see at least 150 volts when cranking. As measured by a special "peak-reading" voltmeter. Less than that, it's likely bad. I've seen stators that seem to output proper voltages, but when warmed up-caused problems. Keep in mind that weak ignition components tend to act up once the engine comes up to normal operating temps. I've seen them test good (barely), but after the engine warmed up-a periodic miss occured. Every 3-4 rpm's it would miss. On random cylinders. A new stator cured the problem. You might try to retest the stator when it's warmed up.

Re: The never ending weak spark saga

Also weak magnets in flywheel can cause this .. I have been told they wont go bad but they do as the 1988-93 V-6 is notorious for weak hub magnets. If its firing on all 4 cylinders you can eliminate the sensor base. Its going to be a stator, pack or flywheel problem

Re: The never ending weak spark saga

We bought a stator. It seems as if this is the last piece of the puzzle considering the fact that we have replaced the coils, plugs, wires and power pack already. Hopefully it works. We just wanted some reassurance that the stator was the problem before dropping the money on it.

Re: The never ending weak spark saga

have you tried running on xd-100 oil...or similar synthetic oils

more expensive but.... may help a bit....

it also contains decarbing ingredients

Re: The never ending weak spark saga

Just a thought, have you check your thermostat?? If, it has failed in the open position, then water will be circulating through the water jackets and keeping your motor much cooler. The motors without thermostats and cold water often experienced plug fouling.

The thermostat keeps the head at a much warmer operating temperature even with trolling. The much warmer operating temperatures allow for better combustion,fuel efficiency, and 2 cycle oil burning. Doing a lot of trolling with a cool head will accelerate plug fouling.

Check your head temps with a infrared digital thermometer and if the temps are not staying in the the 130's to 140's after being warmed up then your thermostat may have failed in the open position or if this is a new to you motor, there may not be a thermostat. Someone could have removed it at one point for what ever reason in the past.

Cheap consideration and it cost you nothing to evaluate. I may be off the ball, but hey, it will cost you nothing.

Re: The never ending weak spark saga

Hmmmm. I'd consider a little 4-stroke kicker for trolling instead of a 2-stroke running at idle, or near idle, for prolonged periods.

Re: The never ending weak spark saga

the early 135's were not the best idling outboards when compared to the 85's and 115's of their era. The "baby butt" tuned exhaust and the aggressive porting of the cylinder block did not make it a great trolling motor.

If the pistons, rings, and walls are in good shape, do 2 decarbonizations of the motor following the directions on the Evinrude Engine Tuner spray cans. Then use Champion QL77JC4 plugs gapped to .030". In extreme cases, the QL82C plug works well for extended trolling.

Re: The never ending weak spark saga

The factory recommends the surface gap plugs for the 135-140 hp engines from 1973-1984. UL77V.