Saw died, stinkin spark plug!

I ran my saw last night as I packed up so I could cut wood today. It idled fast and sounded rich at wot, then it died like it was shut off. I checked the gas, it was low. Nothing really strange about that, except the richness at wot. I didn't think too much of it because it started right up after fueling. It was a little strange how fast it quit, but I dismissed it.

It died again today after a few cuts and would not restart. I checked the plug, it sparked good, but the plug was dry. Ok, it needs a carb kit. No biggie. I packed up and came home.

I was sitting here tonight thinking about it and decided to take a better look at it. The plug was nice and wet! Checked spark, nothing, stone dead. Ok, maybe it's a bad coil....hope not. I'll try another plug. Bright blue spark! Put the new plug in and it fired right up and idled perfectly. I didn't let it warm up, so I don't know how it will do at wot, but I think the plug was the problem. It was an off brand....never again.

I'm excited to run it again tomorrow if the weather is nice. Supposed to be rain moving through.

 

Glad to hear it was a relatively easy fix!

 

I messed with a saw for a good while before I found out the insulator was loose in the hex shank of the plug causing it to loose compression and fire erratically or not at all. First and only actual plug failure I have really had. Now I have pulled many worn out plugs but they still fired.

Always nice when it's something simple, but sucks cause its usually something as simple and reliable as a hammer so you don't give it much thought at first.

 

This is the second plug failure I have ever had, and it's probably chinesium. The first was about 20 years ago. I was running the snowblower and there was a really loud bang and it quit. Still had compression, still did everything except run. I tore it down, didn't find anything, and it still didn't run. Turns out it was the plug! No idea what the bang was...

 

I've had extremely good luck with NGK plugs in OPE engines...and bikes.

 

The rain let up for a bit today, so I ran the saw to make sure it was actually fixed.

It was a night and day difference from when the old plug was still working. The saw would hold about 12,500-13,000 rpm in the cut with the old plug. I thought maybe the replacement piston wasn't sealing well with the used ring, because it used to run even faster/stronger.

With the new spark plug, it's right back to 13,800 in the cut, and it's not side gapped yet AND it's a bit rich. I'm looking forward to cutting a LOT more firewood now! The rakers are already at .030". Might have to file off another .005-.010".

 

I had a 1985 GMC S-15. I had changed the plugs and about a week later it started running like crap. I thought it was bad gas. I tried dry gas, fuel treatment, etc but no luck. One day I had the hood up with the engine running and I kept hearing SNAP SNAP. I looked closer and you could see the spark from one of the new plugs running down the outside of the porcelain to the engine. I fished one of the old plugs out of the trash, replaced the plug, and it ran fine.

 

Let me guess, Champion?

 

Don't remember the brand.

 

I think that's what was going on with the saw. There is a burned spot on the porcelain where it meets the metal body.

 

Glad that fixed it. It's miserable when you've done all that work and a simple spark plug has you guessing everything you touched. FWIW I replaced the plugs in my pickup with NGK's and it ran noticeably worse. I put the originals back in and it fixed it. Had a lot of replacement parts lately fail. It's the times we are living in, lots of stuff is junk even from name brands!
Brad

 

I've been using the Denso plugs in my saws for a bunch of years with great success. I've never fouled one as they get replaced on a pretty frequent schedule. My big saw came with a champion plug and I did run it for a little bit, till it started acting up. Pitched it and ran NGK for a while and never had plug issues since. Well, I did have one failure, the insulation around the electrode broke free causing a no-start situation. Change of plug got it going, then I noticed the issue.
https://youtube.com/shorts/tl705AlC_rk

 

I have had an ngk in my stihl 390 for 14 years. I have only removed it once, and that was when I ported it.

 

Sorry, I just checked and it is a bosch plug.

 

I side gapped the spark plug in the 350 today. It is an ngk. (My 390 is a bosch) I dug out a bosch too and side gapped it, just to have a spare. Side gapping changed the tune and took the richness away. I ran it with the ungapped plug at the same carb setting and it was pig rich. I think that's where the 13,800 rpm came from. Then I ran it with it side gapped and it sounded perfect. Giving the flame kernel an open path must make a bigger difference than I thought.

I cut some oak and it was holding a pretty solid 13k in the cut, so I'm happy. This chain is the same one I used in the elm, so it may need a touch up, but it's still pretty dang sharp. I'll swap chains tomorrow and see how it does. I have a pile of oak trees to clear out of a friend's yard.

 

What is side gapping??

 

X2

 

Another vote for Denso plugs . Never had an issue with them .

 

Does Side-Gapping Spark Plugs Work?

 

Ahh….. thanks!
Next question: how many people here do it on their saws?
3rd question: is the difference noticeable?