Like many of you I have been turning wrenches a very long time.
I went to mow my lawn, non Corvette issue on this one.

The Honda mower fired up first pull as it does most times.

Ran perfect for about a minute then started coughing and dies.

I figure crap, water in fuel. It has happened before. Drain the fuel, drain the carb, install new fuel. Pull rope, starts first pull runs like a top. About one minute later it dies again. I know tank is clean and fuel is fresh so I pull the plug, looks fine, not wet. Check the gap clean it, hook up the plug wire, ground it and pull the rope. Great spark.
I rule out spark. Install the plug pull the rope it runs perfect for another minute then coughs and dies again.

OK, I figure something in the carb is plugged. Pull the carb tear It down clean everything and re install. Pull rope, fires up perfect and I figure I did a great job. Then it dies again after about a minute.

Now I am ticked and wasted a lot of time, it is now dark, can't mow the lawn and I hate to lose a battle with a machine.

I try to start it again right after it dies and it will sputter but not run.

I grab the ether, starting fluid. I very well know I can blow a piston right out of the block with this stuff so I am careful. Pull rope with starting fluid in the carb and NOTHING. At least now I have direction the spark is going away after start up but comes back after short cool down.

I go on line, google I expected the magneto or electronic ignition module was out.
Google: Honda dies after start up. Guess what. Article states the OEM NGK spark plug does exactly what I experienced when they go out.
In all my years I have never seen a spark plug come and go. Work cold and die as soon as heat builds in the plug. In my years they work till they die or get weak because the electrode wears out and the gap is too large. I have never seen one come and go. As a kid I wore out 3 mini bikes and a couple motorcycles all ran one spark plug. Never had this happen.

I checked my available plugs in the house since it was nearly 10PM now and I had a set of old FIAT Spark Plugs from my wife's old 124 spider. They were almost a perfect match for the Honda NGK plug. Yes I can compare spark plugs pretty well. The heat range was nearly identical.
Put in the plug and Bam, fired right up and runs smoothly.
One positive note, my choke had been sticky for the last 5 years and now it works like new again.

This is not about Corvettes but I think it exposes an issue that we might run across with our old cars.
If some of you knew already of this issue I bow to you and wish I had known. I will take NGK off my shopping list.
I will get a Champion plug today and replace the Fiat Plug, odd the Fiat Plug was an AC Delco branded plug.

One more item to consider when the car starts to misfire or randomly drop a cylinder.

Mark

 

Mark - That's a helluva lesson alright. I too always figured a plug was either good or bad, no in-between. What I take away from your story is to keep an open mind as to possibilities. Glad you finally got it figure out.
Mike T - Prescott AZ

 

I won't quit using my NGK-XR4 plugs in my Chevy small blocks on the basis of a google search and a misfiring lawnmower. Simply the best plugs I've ever used. I'm just sayin'

 

That's interesting. It's obvious that spark plug temperature is at a point where the plug fails but I'm not exactly sure why. Is it a resistor plug?

Some resistor spark plugs have what was/is called a booster gap in the upper metal rod portion. The gap intensifies the spark. (and reduces FM radio static)

Other resistor plugs use the upper section of the core rod itself as a resistor with different metals with higher resistance values. Is it possible that the resistance value increases beyone the energy level of the spark when heated? I don't know but I can't think of anything else that could cause this.

But that same spark plug functioned just fine for quite a while before this issue started so I have to guess that something changed in it's resistance value from... heat cycles??

I bet that same spark plug would function properly in an engine with hotter ignition?

 

It is in a lawn mower with limited electrical power to make the spark for sure.
Odd to me that it started each time on the first pull even though it was a cold engine but died within one minute and would not re start.
You might be right on the cause, newer Lawn and Garden Plugs do have EZ start technology to boost the low voltage spark and help with cold starts. The plug did work well for years prior to this.

 

I learned a long time ago playing with honda bikes that NGK plugs don't like to sit around during the long winters. Intermittent failure under compression and unexpected breakdowns used to **** me off so much that I just replaced them every spring to avoid the trouble.

 

My JD rider had similar issues, twice.

Check that the fuel cap vent is open,
and the other was a bad coil. Would run and start when cold but die and not restart when warm/hot.

 

This would be my guess as well. Still, it's hard to argue that if changing the plug would correct the problem. Maybe it's just masking the problem?

I've had NGK plugs in small engines in OEM application but never seer or heard of this problem with them.

 

After changing the plug it has fired and ran perfectly every time since with no stalls. I mowed the lawns last night so it ran for over an hour and no issues at all. When this was happening I did loosen and even remove the fuel cap with no rusult and there is a drain plug on the carb bowl that I loosened and confirmed I had fuel after it had quit so fuel was available. It was the spark plug. I looked for the spark issue after spraying starter fluid into the carb right after it died and starter fluid had no effect when I pulled the rope. Normally starter fluid would fire so hard you would hear detonation. If I let is sit for 5 minutes which cooled the plug it would fire up like brand new and run and sound perfect for almost a minute and then cough and die.

 

Put the one back in you had problems with and see if still acts up.

 

Exact same thing on my old (circa 1999) JD.

Wes,

No doubt it was your NGK plug, and obviously a heat related problem.

I have seen some strange plug issues, but not that one (Champion plug failed right out of the box - center electrode was "grounded" & Bosch plugs that had the center electrode "disappear" over time of usage).

Plasticman

 

Enjoyed reading your story.....

I have to ask: How about putting the NGK plug into the wife's Spider and sending her out for a spin??

 

SD that is funny, I did better than that, a young couple made us an offer on the old 124, which was a very pretty car in great shape and we took the cash and they drove off in it, a year ago. But I still had spare spark plugs! I looked up the cross reference and the AC Delco Fiat plug is cross referenced to the NGK so my eye was accurate.

To verify the plug failure, and appease those with interest I fired up the Honda today. It started first pull and ran perfect like it did yesterday when I was able to mow the lawn.
I pulled the spark plug, it had a nice light grey burn pattern and re installed the NGK that gave me the headaches, had to pull it our of the trash can for your entertainment. The Honda fired up on the first pull with the NGK in there but ran perfect only about 15 seconds then coughed and died. I suspect the shorter run time was the result of installing in the warm engine rather than a cold engine.
It would not re start after it died.
Pulled the NGK and put in the new plug. Started second pull, maybe a little flooded, and ran like a top.
The Google boys were correct, when the NGK goes out it will fire perfectly cold and quit when it warms up. I never expected the plug to work like new cold and then shut off as soon as a little heat hits it. I have never seen a plug do that.
I hope this provided some entertainment.
Mark

 

Mark,

You may be on to something. My son's kart and Briggs board track bicycle forums have listings of vintage plugs to keep, and warning about modern mower plugs to avoid (even with the Predator OHV Honda clones).

All I know for sure is my son often "borrows" the used NGK-R plugs from my 350 with the aluminum Bowtie heads and a stack of indexing washers to fit his engines.

 

I had the exact same issue with my JD, the gas cap not venting.

 

How about this: Use a multi-meter to check the resistance from the terminal to the electrode when cold. Repeat when hot.




The suspense is killing me! (it's a slow day at work)

 

Yes, that's the internal gap in resistor plugs that I mentioned earlier. They call it interferrence suppression. If, for some reason, the gap increases, it could cause an issue as the spark would have a greater distance to jump across. The gap increases spark intensity but if the gap is too wide, it may not jump the gap at all.
I have no idea as to why the gap increases though. Is there a carbon link between the upper and lower elements?

 

The next time you buy AC Delco plugs, per GM, check to see who makes them. Most likely you see NGK and you even may see a NGK number.

 

I know that, AC has not made spark plugs since the early 80's. Champion had several AC contracts over the years. You are correct if you look at the machining and tool marks and stamps on the plugs you can figure out what plant made them.

 

You can't make this stuff up. I just got a call from one of my best friends. I've been building his race motors for 30 years. He says his wife went to pull their nearly new mower to the house because it quit with his Can Am side by side. And it's missing. He says well the coil pack has gone out on the CA but he switched cylinders and the miss followed the plug. Before he gets hardly any of this out of his mouth I'm asking if they're NGKs. He says how did you know that? I told him about reading a thread about this very thing yesterday.