My 066 eats spark plugs

[Ada Shaker]

I have been a licensed amateur radio operator for about 35 years, so I understand the concept. But, I was thinking the resistor plugs were designed to limit interference to AM radios in cars where the wanted signal and unwanted interference are amplified equally. In todays technology it may interfere with the onboard computers etc.  FM and digital are not effected to the same extent at all. Plus antennas are a two way street, so I can't see a chainsaw bothering anything ever even in the AM days for more than a few yards maybe.

But, it could be that all they make are resistor plugs anymore for simplicity or other reasons that don't occur to me. May interfere with the electronics in the ignition module itself.

The reason is not RFI from chainsaws.

Chainsaws and other combustion engines are unlikely to produce much RF as stated earlier as the spark plug is encased in a closed engine. Or better said, the RF from the spark would have little interference if any due to it being encased/shielded in a metal enclosure. You'd probably get more RF from an old chainsaw that used the points system that had little shielding, but most saws of those days were pretty much all metallic anyway. Tx Rx antennas are 2 way but tv and receivers are 1 way. I would imagine Rf would have some effect on the Rx circuit in some way, perhaps at some frequencies more than others.

As far as the resistor spark plugs go, they may form part of an LCR circuit within the ignition circuit itself. The R portion limiting current flow when the circuit hits resonant frequency (only taking a guess here) when XL=Xc when the chainsaw hits full speed for cutting. Like i said I'm only taking a stab in the dark, as there isn't much information out there on the design of chainsaws and its all kept fairly secret. Your Tx Rx radio circuits also use resonant frequencies to tune into a particular channel sliding along the frequency scale, its that resonant frequency that determines what channel your on.

I really couldn't think of any other reason for having resistive spark plugs other than for RFI suppression and/or being part of an LCR circuit where it interacts electronically with the inductance of the coil and the capacitance of the condenser/capacitor.

My background is that of an electrical fitter, electrical mechanic, have some studies in the realm of electrical/electronic engineering, and recently added to this, a diploma of visual arts (majoring in photography) which has nothing to do with chainsaws but i can take some pretty pictures of one if you like. :D :D :D

[ZeroJunk]

Just reading around there seems to be some thinking that a non resistor plug can fry an electronic ignition. Resistor buffers the discharge. I can see some logic in that.

[Ada Shaker]

Just reading around there seems to be some thinking that a non resistor plug can fry an electronic ignition. Resistor buffers the discharge. I can see some logic in that.

Yep, the old points ignition had a straight out spark plug with steel ignition lead. The new leads are so floppy these days, id say they're some form of silicon/carbon or some composite material. Vehicle ones are very similar these days in flexibility and also have some resistance to the leads. Adding to this its quite possible that the coil has some resistance in series with its lead. I can't really say as I've yet to measure coil dc resistance but i would imagine it would be fairly low ohms, the lead could possibly bring it up some what. Some one might be able to compare a points coil resistance with the resistance of an electronic ignition module to verify if this is correct.

[Al_Smith]

A lot of the old plug wires were braided copper with non shielded insulation .Then they went to carbonized conductors with semi conductor shielding etc good for around 100 thousand volts .Prevented flash overs,cross fire between the plugs etc .The plugs last almost forever any more .

The noise on radios TV etc was picked up by the intermediate frequency transformer and amplified to the speakers .Often the video picked it up and the TV acted like an osciliscope which drove people nuts like a pass play,fourth down 20 seconds to go on a football game .All they heard was buzzzz.

I'm not sure any of the above has anything to do with a chainsaw ignition system .

[Al_Smith]

Now here's what might be happening .Some Stihls,042 and 048 for example with SEM ignitions had self advancing coils .If for some reason the advance solid state circuitry failed it might just be cutting off .There no repairing just replacing .I have no info on the saw ignition in question so it's a stab in the dark .However I've had advancing coil types either fail on full advance or fail to advance and either condition  causes problems .

[ZeroJunk]

Now here's what might be happening .Some Stihls,042 and 048 for example with SEM ignitions had self advancing coils .If for some reason the advance solid state circuitry failed it might just be cutting off .There no repairing just replacing .I have no info on the saw ignition in question so it's a stab in the dark .However I've had advancing coil types either fail on full advance or fail to advance and either condition  causes problems .

Not a terribly uncommon problem on newer Stihl blowers and trimmers.  I have replaced, rebuilt carbs because the unit just won't take the throttle only to find out the ignition was bad. Idles fine, so I am assuming it lost it's advance.

[Canadiana]

In the dark if you connect your spark plug and ground it to the cylinder, then pull starter you will see spark. Alter the new one with a dead one. Watch closely for a small difference in spark. This may give you another clue but this issue is beyond my skills n experience. Very interested to hear how you solve this. Best of luck

[joe_indi]

If you are using a NGK or Bosch plug an your ignition is weak, the spark might be quite weak. But, if you can lay your hands on one of the cheap plugs that come from China, chances are they are unsupressed and their spark would even put Darth Vader's stun gun to shame  :D. And on a weak ignition coil they work quite well. I posted quite some time ago about even using them to 'force start' engines with temporarily stuck rings.

[Scott03]

Just got my saw back from the shop, and it works like it's supposed to.  So far.  But...

Nobody really knows why, for sure.  The mechanics didn't know what to make of my story:  Brand new plug quits, replace it with another and it works, until it quits, too, after just a few tanks of gas.  Rinse and repeat.  Then put the "dead" plug in my MM55 tiller, and it works, but put it back into the 066 and no go.

They actually asked me:  "What do you want us to do?"  To myself I thought "You guys are supposed to tell me!"  Out loud I said "How about giving it a good tuneup, and check the ignition system and coil?"  That made sense, so off they went.

New air filter, fuel filter, and plug.  Ignition system and coil checked out as normal.  The kill switch didn't stop the engine, once, so they fixed that.  The carb was running a bit rich so they adjusted that and put a tach on it to get the high end right.  New clutch springs.  Then they cut with it for 20 minutes and proclaimed it good to go.  I worked it another 20 min. or so when I got home.

There you go, guys. I wish they'd found something specific, so there was a better sense of finality about solving the problem.   

[Ada Shaker]

Just got my saw back from the shop, and it works like it's supposed to.  So far.  But...

Nobody really knows why, for sure.  The mechanics didn't know what to make of my story:  Brand new plug quits, replace it with another and it works, until it quits, too, after just a few tanks of gas.  Rinse and repeat.  Then put the "dead" plug in my MM55 tiller, and it works, but put it back into the 066 and no go.

They actually asked me:  "What do you want us to do?"  To myself I thought "You guys are supposed to tell me!"  Out loud I said "How about giving it a good tuneup, and check the ignition system and coil?"  That made sense, so off they went.

New air filter, fuel filter, and plug.  Ignition system and coil checked out as normal.  The kill switch didn't stop the engine, once, so they fixed that.  The carb was running a bit rich so they adjusted that and put a tach on it to get the high end right.  New clutch springs.  Then they cut with it for 20 minutes and proclaimed it good to go.  I worked it another 20 min. or so when I got home.

There you go, guys. I wish they'd found something specific, so there was a better sense of finality about solving the problem.   

Good to hear you got your saw back and there was nothing seriously wrong with it. In your opinion, do you think the saw may have been running a little hot?. I've known engines to run hot when the air filter needed replacing so maybe this coupled with a fine tune will hopefully solve your problem. Just out of curosity, has your new spark plug changed resistance since running the saw?. This may give some indication that the problem may have been an overheating issue to begin with.

[Scott03]

[/quote]

Good to hear you got your saw back and there was nothing seriously wrong with it. In your opinion, do you think the saw may have been running a little hot?. I've known engines to run hot when the air filter needed replacing so maybe this coupled with a fine tune will hopefully solve your problem. Just out of curosity, has your new spark plug changed resistance since running the saw?. This may give some indication that the problem may have been an overheating issue to begin with.
[/quote]

I don't think so, even though I was kind of hoping it was, because that might have explained a few things.  The "dead" plugs I would change out all had carbon deposits on them, like it was on the rich side, and the shop guys said that, too.  Isn't it when the carb is too lean that you get too much heat?  Also, the mechanic didn't think the filter was particularly dirty, he just thought it would be on the safe side to replace it.  I still have it, it's the washable type so I'll keep it on the shelf as a spare.  Good point about the resistance, I didn't think to measure it.  Will do that before I run it again. 

[CTYank]

Those carbon deposits on the insulator can have the spark current bypass the spark gap.
A useful tool in cases like this is an inline spark checker. You connect one side to the cable, the other to the plug. The transparent center part has a gap where you can watch sparking. Soooo, while running, you could see the normal spark, and then watch it when/if the engine acts up to see if the spark dies first.

[Mountain_d]

I agree. I would bet on a weak ignition coil. Mountain.

[joe_indi]

It would be advisable to examine the ignition lead (for frayed insulation) ditton the short circuit wire, and the torsion spring in the spark plug boot. It is notorious for wearing out from vibration, just enough to prevent constant current.
All of these or one of them would cause erratic spark at the plug, which in turn could cause carbon buildup or an oily plug

[beauj5]

Did you ever resolve the problem with the 066 going through plugs?

[Al_Smith]

This is a mystery .As per that pic for some reason the electrode insulator is becoming carboned up for some reason .It probably creates a short circuit from the electrode to ground providing a lower resistance to ground than jumping the gap.Obviously the spark will follow the path  of least resistance.

Now the big question is what is causing the carbon? Could is possibly be the fuel?

[DelawhereJoe]

What mix ratio do you use in this saw and what oil in the gas ? I'll also assume you use the same mix in other saws with no trouble.

[Al_Smith]

It's confusing to me because even running a ratio of 16 to 1 on old outboard boat motors  it didn't foul the plugs .About the only thing that would is running at trolling speeds for an extended period of time .Then all it was was to lean out the high speed a tad and run the snot out of it  then get back to trolling .

I'm not certain if some of those gas additives would cause this or not or even if they were used .If so that may explain a few things .

I have some saws I've owned for over 30 years that have the original  plugs .Now I might have wire brushed them a time or two while doing routine maintenance which isn't all that often but they've never been replaced .

[Mountain_d]

I was having a similar problem with a snowmobile just last week. I read on a snowmobile forum someone was claiming they solved this by replacing the cylinder base gasket. I not sure the logic behind it but something to consider. Mountain.