new coils & plugs -> plugs failing

i just replaced my coils with sierra replacement coils for my 1971 evinrude 50

after all sorts of trouble shooting i've found the problem to be an intermittant sparkplug.

the plug is a QL77JC4 both are brandnew, 8 hours use.
obviously i will buy more plugs and keep replacements handy.


what causes new plugs to fail? are there alternatives to the champion plugs or a different series i should be using?

back in the day, if i burned a plug in my dirtbike; i went up or down a number in the same series of NGK plugs. does this hold true for outboards?

are there many alternatives or did i get a bad plug?

Re: new coils & plugs -> plugs failing

Very rare I should think but it is poaaible to get a bad batch of plugs.

Long time ago now but I bought some (Champion) plugs from the Car club at work and had trouble with them after a short time and with a replacement set although the old ones put back in were fine. They eventually sent the whole box full back to the supplier. New ones fom a new batch were no trouble.

Re: new coils & plugs -> plugs failing

Cross-reference for the QL77JC4 is the NGK BZ7HS-10 (re-gapped down to 0.030").

Re: new coils & plugs -> plugs failing

1971 ignition, is that a 'points' ignition?

A worn rubbing block and too tight a gap or dirty points will cause intermittant failure.

Clean and gap the points, replace if pitted.

Re: new coils & plugs -> plugs failing

BRP is listing the Champion UL77V surface gap for your model at this time.

See your Cylinder & Crankshaft diagram here: http://shop.evinrude.com/

Re: new coils & plugs -> plugs failing

if you used the put together sierra coils and wire, i have found if you do not do it correctly, you get intermittent spark. i cut back the insulation on the plug end, and wrap the wire around the spring. also be sure the pin in the coil, hits the center core of the wire..

Re: new coils & plugs -> plugs failing

CharlieB said:

1971 ignition, is that a 'points' ignition?

A worn rubbing block and too tight a gap or dirty points will cause intermittant failure.

Clean and gap the points, replace if pitted.

Click to expand...

no its magneto.

Re: new coils & plugs -> plugs failing

bought new QL77JC4's again and managed to do 2 whole miles

(1/2 throttle, 1 mile out, 1 mile back, with 20 minutes of trolling.)


what causes sparkplug failure. i have brandnew coils... could my timing be off? i cant figure out why the plugs are failing.

Re: new coils & plugs -> plugs failing

Could you give a bit more of an accurate description of the plugs after use, pics may be handy as well.

Different plug conditions will lead to a different diagnosis.

Re: new coils & plugs -> plugs failing

JT! said:

what causes sparkplug failure. .

Click to expand...

I am assuming that your plugs are fouling. The cause of this is basically carbon building up on the insulator creating an effective short between your electrodes. When this happens the electricity stops arcing across the electrodes and you now have no spark to ignite your fuel.

Now the next question is: why is this carbon building up on your plugs. This comes from improper burning of the fuels which can come from a number of things. I won't bore you with any more of the science, but if I were you I would check the following in this order:

1) Are you using the correct plugs
2) Are the plugs gapped properly (do not just take them out of the package and screw them in, as a lot of people do. Ensure the gap is correct)
3) Is your carburetor's rich/lean adjust properly tuned. I would start your motor, let it warm up, bring it to a slow idle and then slowing turn in your slow speed adjust clockwise about 1/8th of a turn at a time. If the motor starts to sputter and pop after about 1/4 turn, then I would turn it back to where is was and say ... yes, this carburetor is properly tuned. If it takes 3/4 of a turn or more I would say ... I was running way too rich and that may very well be why my plugs are fouling. I would then search for Joe Reaves carburetor adjustment procedure and ensure this is set properly.
4) Does the motor have a good powerful spark. Can the motor's ignition jump at least a 3/8 inch gap. You will need a spark tester for this. Just observing a spark is not enough since it must jump this gap in order to prove that it is supplying the necessary voltage to spark effectively in the compression environment that exists in your cylinders.
5) Is the thermostat working properly. If it has failed open, your motor will run cooler, again causing an improper burning of your fuel. This condition will build up carbon in your cylinders and eventually start fouling your plugs.
6) Is the motor all carboned up already. Here I would just search this forum for "decarbing" your motor and perform this procedure.

I doubt you are continuously getting bum plugs. It is more likely one or more of the above conditions exist. Good luck to you.

Re: new coils & plugs -> plugs failing

i hadn't thought to check my thermostat.

i will also undo my timing screw changes and try re-tuning the carbs, as i'm remembering now it was very chilly the day i last tuned it (at 5am) and lately i've been out in warmer hot sunny weather. i will follow Joe's guide to the letter.

Re: new coils & plugs -> plugs failing

JT! said:

i just replaced my coils with sierra replacement coils for my 1971 evinrude 50

after all sorts of trouble shooting i've found the problem to be an intermittant sparkplug.

the plug is a QL77JC4 both are brandnew, 8 hours use.
obviously i will buy more plugs and keep replacements handy.


what causes new plugs to fail? are there alternatives to the champion plugs or a different series i should be using?

back in the day, if i burned a plug in my dirtbike; i went up or down a number in the same series of NGK plugs. does this hold true for outboards?

are there many alternatives or did i get a bad plug?

Click to expand...

Why do you think it's a plug failure and not some other problem? I'm no expert, but I've had intermittent spark caused by other factors. (merc - bad coil and bad switchbox both caused that problem for me).

Re: new coils & plugs -> plugs failing

dajohnson53 said:

Why do you think it's a plug failure and not some other problem? I'm no expert, but I've had intermittent spark caused by other factors. (merc - bad coil and bad switchbox both caused that problem for me).

Click to expand...

the problem has spanned over a few threads as its presented itself a few times. the coils are new, and were also a suspect at one point.

i have systematically checked the plugs to the point i know the plug is fouled, as i can switch them, and run on the other cylinder. and using a known good spare, i can be back on 2 cylinders.

but throwing plugs at the problem doesnt help, i've determined i must be soaking my plug (just the 1) while im trolling. then any attempt to resume speed is just not possible.

it took a few outings to see the pattern of events.

Re: new coils & plugs -> plugs failing

By the way. On my point 6 above. You should perform this decarbing procedure on a regular basis but especially after you have experience some fouled plugs. If you think about it, if plugs foul because too much carbon is getting layered onto them, you have to believe this carbon is getting everywhere else as well. All over your pistons, cylinders and especially your piston rings.

Once you figure this out, you should get rid of that carbon as soon as you can. Here's the procedure link. Good luck.


http://forums.iboats.com/showthread.php?t=158076