Is my problem the spark plug?

[StihlsawuserMS361]

I found as being a GM mechanic for over 30 years, something usually causes the spark to fail. We had back in the day some plugs which the porcelain insulator would loosen up, causing a misfire. Scope the engine, pull the plug, look at the electrode up, looked fine. Reinstall, same skip. Pull plug again, look at it differently (sideways for some reason), saw the loose porcelain which when installed blocked the electrode. Usually only get bit once on something like this.
I always use OEM plugs, whether AC, NGK, Autolite , Champion etc... Found too many times GM's didn't like Champion plugs for some reason.

 

[Howsitgoineh]

“it must be the spark plug”. Well, no. It most likely isn’t. I’d say you have a single digit percentile the spark plug is actually the problem.

Got to watch those words most likely not.
I lot of people that think they are really good mechanics and work on a piece of eq that has only one spark plug like for example a chainsaw for several days tuning the carb, overhauling the carb, pressure testing the crankcase and then it seems they have eliminated everything EXCEPT that little old measley $2 spark plug they stick another spark plug in and surprise it runs great.
They are so great of a mechanic that they will not admit to anyone else that it was JUST THE SPARK PLUG after they spent hours or days trying to fix the equipment. They really do not want to admit it to themselves.
They want to keep it a secret because good mechanics just don't overlook simple things.
Changing the spark plug to the correct one is one of the easy things to try first but often overlooked because you are a great mechanic and do not have time to fool around with doing something simple as a fix.
I've seen a bad $2 spark plug fix a piece of eq often enough that I check the plug often when a piece of eq is not acting correctly. Really makes me feel weak upstairs if I overlook a measley little spark plug as the problem.
I've actually got some bad ones in a box labeled bad just to show people. Mostly the little j6-j8 champions that look good visually. I would like to install some of these bad plugs into some engines that are being used in a small engine mechanics class and watch the results or even a piece of eq headed for a PRO mechanic technician shop and then listen to the results of the troubleshooting procedure for a fix. Most likely the spark plug would not be mentioned.

Don't forget to put fuel in it

 

[bwalker]

Spark plugs can wear out. When I owned my fishing lodge boats would get about a year give or take on a set of plugs. The gaps opened up so much by that point that they became hard to start and didn't want to troll or idle smoothly. Many times these machines where operated from 6 am to 10 pm more or less consistently for 4.5 months of the year. Lots of hours.
In a chainsaw this just isn't happening, especially with guys on this site.

 

[lone wolf]

So you hear this EVERYWHERE. “My chainsaw (or any other small engine equipment) wouldn’t start, so I tried changing the spark plug!”

I’ve never had this be the root cause of a problem. Clogged intakes, poor fuel, leaks, bad tuning…sure! You might pull a spark plug and be amazed at how it’s running with such a gunked up part, but if anything, it’s telling a story about another problem. Hit it with a brass brush and put it back in, then fix the actual problem!

How often have you had just changing the plug fix a starting problem? Curious if I live in some kind of micro-universe with different rules.

I had one that the porcelain was cracked on it and that would not let it start! At first, I was thinking no fuel!

 

[grizz55chev]

If yer chasing a problem like a miss fire at mid to high rpm,, always start at the beginning. To not change the plug is like taking a shower and not putting on clean underwear.

 

[mudrat2]

Had a failure like this one time on a twin cylinder garden tractor. Plug looks fine when you held it up to look at as the ceramic slid down into place. Hold it spark end down and the problem shows up.

 

[sean donato]

Had that happen on my wife's focus when she was coming home from college for a long weekend. Called me about an hour away in the turnpike, cars shaking but still moving. She drove it to the next interchange where I met her with the truck and trailer. Screwed around with it once we got home. Can't remember what cylinder it was, but sure enough one of the insulators had cracked off and slid down. I wanted to be mad, but I'm pretty sure it was all original to the car at that point. Car had to have over 160k miles on it by then. Just did all 4 plugs and a set of wires. Done deal.

 

[StihlsawuserMS361]

Sometimes a plug won't misfire until there is a load on an engine. Single cylinder two stroke, simple, one plug. Multiple cylinders....

 

[OM617YOTA]

Modern plugs and ignition systems are so good that it's really easy to forget the basics. When I did a tune up on my truck shortly after buying it, the GM HEI was still firing the plugs just fine, even with most of the ground electrode burned away, well over 1/4" spark plug gap.

 

[Howsitgoineh]

While we're on the topic of spark plugs here, what is the optimal spark plug gap for a chainsaw?

 

[Tomos770]

0.5mm

 

[James G]

Make sure you got a legit NGK. NGK even has a counterfeit identifying page on their website. Buy from eBay or Amazon, who knows what you really got.

Amazon takes pride in selling cheap Chinese crap and they will not tell you where the **** comes from.

 

[pioneerguy600]

I have been a two stroke junky since the early 60`s and have had only a couple bad plugs in various equipment, internally shorted ones and a couple broken insulator ones. Also had a few that wouldn`t fire consistently in one engine but would work perfect if swapped into another, this swapping often occurred in remote areas far from available replacements, new plugs would be installed at the earliest trip out to civilization. Fouled plugs were quite common as some engines set for long periods with old fuel in them and often ran a very rich mixture, even had carbon particles break off in the combustion chamber and lodge between the electrode and plug body causing a short.

 

[stihltech]

Just replace the plug with OEM. Problem averted and/or solved. If you can prove it is not the sparkplug, you can always reinstall it.
But WHY would you.
Do the easy stuff first.

 

[Sidecarflip]

On the subject of spark plugs, I wonder what happened to the specialty plugs like Splitfire's? They were the rage back in the 60's when I was younger...lol

 

[HarleyT]

Have you ever noticed that the guys that get involved in a lot of spark plug threads,
are usually the same guys involved in the thread repair threads?