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Author Topic: My 066 eats spark plugs  (Read 7432 times)

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Offline Scott03

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My 066 eats spark plugs
« on: October 20, 2016, 10:31:01 AM »
Lately, my old Stihl 066 has been acting up.  After checking fuel-related stuff - filter, carb settings, etc. - to no avail, I tried changing the plug.  It started right up and ran fine.  But only for just a few tanks of gas:  It quit again, and a new plug fixed it again.

Yesterday, with the new plug installed, the saw ran about 2/3 of the way through the tank before quitting once again.  With still another new plug, it ran again and I finished the day's work, but by the end of that same tank of gas the saw was idling bad and acting like it wanted to quit again.

Each plug that fails has minor black deposits, so I guess that means it's running rich, but they're not fouled and the gaps look normal.  They look pretty much like what they are:  new plugs.  Except they're dead.

Anybody have any ideas?  I'd like to fix it myself, if I can.

Offline joe_indi

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Re: My 066 eats spark plugs
« Reply #1 on: October 20, 2016, 10:50:52 AM »
Try running it with the switch wire (thin black)disconnected from the ignition coil.
Also check if the spring in the spark plug boot is worn out (loose contact)

Offline Scott03

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Re: My 066 eats spark plugs
« Reply #2 on: October 20, 2016, 11:17:36 AM »
Thanks, will try the first one.  I did think of checking the spring in the boot, and it seemed OK, but will check it again.

Offline ladylake

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Re: My 066 eats spark plugs
« Reply #3 on: October 20, 2016, 05:06:16 PM »


 Could be a weak coil.  Steve
Timberking B20 15000 hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

Offline Scott03

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Re: My 066 eats spark plugs
« Reply #4 on: October 20, 2016, 08:46:48 PM »
I thought of that, too, but doesn't it seem more logical that a plug would fail from too much voltage?  It does seem like it would get weaker as it fails, though.  But whether too weak or too strong, I don't know how to test the coil anyway, or the plugs for that matter.  So, it's either swap in a new coil and see what happens, or take it to the shop and let them sort it out.

Thanks! 

Offline HuckFin

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Re: My 066 eats spark plugs
« Reply #5 on: October 20, 2016, 09:02:03 PM »
Try checking the sparkplug for spark when cold, then rechecking when hot.

Offline Scott03

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Re: My 066 eats spark plugs
« Reply #6 on: October 20, 2016, 09:37:13 PM »
OK.  What I'd like to understand is what is causing so many brand-new plugs to fail, or become intermittent, so quickly.

Thanks.

Offline Al_Smith

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Re: My 066 eats spark plugs
« Reply #7 on: October 21, 2016, 05:21:13 AM »
You must have gremlins or something . :o I've never had a spark plug actually fail in a chainsaw .

Offline thecfarm

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Re: My 066 eats spark plugs
« Reply #8 on: October 21, 2016, 05:50:03 AM »
I can remember putting about 2 plugs into one of my brothers junk mowers. I went down to help him on firewood and had 2 spare plugs with me. Forgot how long it ran each time,maybe 15 minutes,and would not start again. This mower was so old,I think you had to have oil in the gas.  :D
Model 6020-20hp Manual Thomas bandsaw,TC40A 4wd 40 hp New Holland tractor, 450 Norse Winch, Heatmor 400 OWB,YCC 1978-79

Offline ladylake

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Re: My 066 eats spark plugs
« Reply #9 on: October 21, 2016, 06:17:21 AM »
I thought of that, too, but doesn't it seem more logical that a plug would fail from too much voltage?  It does seem like it would get weaker as it fails, though.  But whether too weak or too strong, I don't know how to test the coil anyway, or the plugs for that matter.  So, it's either swap in a new coil and see what happens, or take it to the shop and let them sort it out.

Thanks!




  Coils often fail after they get hot so by time you replace the plug they cool off some and run for a while again.   Steve
Timberking B20 15000 hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

Offline ZeroJunk

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Re: My 066 eats spark plugs
« Reply #10 on: October 21, 2016, 07:14:22 AM »
I think the voltage of a coil is determined by the number of turns and value of the capacitance. Don't think there is anything in the realm of physics that could make it generate more voltage. Plus, automobile spark can be 40 KV or better, more than you will get out of a small engine coil.

Offline sandsawmill14

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Re: My 066 eats spark plugs
« Reply #11 on: October 21, 2016, 07:20:11 AM »
i agree with steve  :) next time you change the plug put one of the old plugs back in and see if it fires :)
hudson 228, lucky knuckleboom,stihl 038 064 441 magnum

Offline HolmenTree

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Re: My 066 eats spark plugs
« Reply #12 on: October 21, 2016, 08:52:14 AM »
There's a intermittent voltage break some where or a bad coil . Never saw a saw burn out new plugs one after the other

What exact brand of plug and model number are you trying?
Making a living with a saw since age 16.

Offline Scott03

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Re: My 066 eats spark plugs
« Reply #13 on: October 21, 2016, 01:07:55 PM »
It's a Bosch WSR 6 F, pre-gapped at 0.5mm, right from the saw shop. 

When it was new I measured 3.82k ohms on my meter, after it went dead it measured 4.82k ohms, if that means anything.  The continuity tester didn't work, even on a new plug, I assume because it's a resistor type.

I went out just now and started up the saw with the latest, still-working plug, and it ran fine.  Then I swapped in the "new" plug that went dead, and it's still dead.  Cranked it until I smelled gas, and no go.  Then put the good one back in, and away it went, no problem.

Offline Scott03

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Re: My 066 eats spark plugs
« Reply #14 on: October 21, 2016, 01:24:12 PM »
sandsawmill14 and huckfin, you can see from my reply to HolmenTree that I just tried that with no luck.  Maybe a sacrifice to the gods of Stihl is in order!  Or a new coil.

Offline Scott03

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Re: My 066 eats spark plugs
« Reply #15 on: October 21, 2016, 01:44:25 PM »
Zerojunk, yes that's the way it seems to me, too.  But I'm at a loss to think up things that would break a plug.  Another thing on my mind is if the plugs are overheating from a leaned-out mixture or something like that.  Something is killing the plugs, because a new plug will work, and when I swap in a new-but-dead one it doesn't work.  That is, the dead plugs seem to be really dead, they don't connect up again internally after they cool down.

Offline Scott03

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Re: My 066 eats spark plugs
« Reply #16 on: October 21, 2016, 01:55:46 PM »
You must have gremlins or something . :o I've never had a spark plug actually fail in a chainsaw .

Yes, I think the answer is going to be a sacrifice to the gods of Stihl!  Or a trip to the shop, which is pretty much the same thing.

Offline Al_Smith

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Re: My 066 eats spark plugs
« Reply #17 on: October 21, 2016, 05:50:45 PM »
How in the world does a person check a spark plug with an ohm meter?

Offline Texas-Jim

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Re: My 066 eats spark plugs
« Reply #18 on: October 21, 2016, 06:54:17 PM »
You can check from where the wire goes on to the electrode, it will give you the ohms of the resistor. Should be around 4 or so. But it really doesn't tell you very much. I agree with the others, its highly unlikely the plugs are failing, id look at something else as in coil. Plugs in cars can go well over a 100,000 miles and even though a saw is dirty compared to a car it shouldn't fail that fast.
What we do in life echoes through eternity.

Offline Al_Smith

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Re: My 066 eats spark plugs
« Reply #19 on: October 21, 2016, 07:27:04 PM »
Okay,never heard of that .However he said 3.8 k ohms to 4.82 k ohms,K meaning thousand .


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