Small Engine Question

[AndyM]

Have a Honda GX240 on a chipper that was acting up (would start fine, run for about 20 seconds and quit). I changed the gas, cleaned the fuel filter, new air filter none of which worked. On a web search another owner of the same engine said change the plug - I did and it worked!

I like to understand these things and I cannot see how a plug would be the source of this problem. I would appreciate any theories.

 

[Eldubya]

Doesn't sound to me like the plug would have anything to do with it. sounds like a fuel delivery issue. When it starts it burns through the fuel in the carb bowl and likely isn't getting replenished quickly enough so it dies. Check your fuel lines from the tank to the carb, make sure there are no leaks or kinks.
Another cause could be the float in the carb is sticking.
Clogged jets is another one.

One of the very first things I would try would be to run some "Sea-foam" through it. It's like a wonder-drug for carburators.

 

[AndyM]

Eldubya, yup I agree with what your saying - that's the mystery - the new plug seems to have fixed the issue and I just don't understand how that could be.

 

[RCW]

With time, the plug's electrodes may become fouled/corroded or crack the porcelain insulation to limit/reduce the spark it creates. I don't think using ethanol gas helps, since it attracts water. Ethanol gas is bad for small gas engines for many reasons.

Also, always make sure the gap meets Operator Manual specs.

Sometimes a good cleaning will restore things; others not so much. I use a butane torch and wire brush to clean them.

With the plug out, you can pull the starter cord to see the amount of spark. Should be bright and blue.

Replacing a plug is always one of the first things to eliminate in a problem gas engine.

Most cars/trucks now come with long-life (platinum?) plugs. Small engine spark plugs don't have the same life-expectancy, in my experience.

 

[AndyM]

RCW - well you can bet changing plugs on my equipment will happen a lot sooner than it has up to now. Plug was cheap so I just replaced it.

The old plug I pulled out actually looked ok - a little carbon but not fouled, gap was good and no obvious damage to the insulator. But maybe the 20 seconds of run time was enough to cause it to act up somehow. I guess I will probably never know.

 

[dlsmith]

The plug probably had a crack in the insulator that would open up when it got hot enough, and let the spark jump to the metal shell.

You might take it apart to satisfy you (and my) curiosity.

 

[Newlyme]

Not sure if this could be the same in your situation but here is what happened to me with an ignition system.
I had a 1976 Chevy pick up truck. One day driving down the road at 55 mph running great the engine just lost all power, it died. A few seconds later while rolling down the road it started running again perfectly. I forgot to mention the loud explosion in the exhaust system before it started running perfectly again. It turns out that the coil was going bad and would start and stop and start again providing energy to the spark plugs.
Could the same thing be happening with your ignition when it heated up?

P.S. The loud explosion I heard was the unburned gasoline that got loaded into the exhaust system at highway speed igniting all at once when the spark returned to the plugs. At the time I was towing a car on a tow dolly working that engine and loaded that exhaust with plenty of gas. It was a good thing that the exhaust system was brand new. That muffler swelled up to the size of a large watermelon!

 

[D2Cat]

You also said at the very beginning you changed the gas. Maybe that was the problem, and it just took some time to get the junk out of the carb and fuel lines.

 

[AndyM]

I will have a closer look at that plug insulation for cracks - spark leakage sounds like an interesting theory. I also think the coil idea is interesting. I did hear some minor backfiring after it quit and I tried to restart it. Not sure how you test a coil.

Thanks for the ideas.

 

[KennysNewFarm]

I will have a closer look at that plug insulation for cracks - spark leakage sounds like an interesting theory. I also think the coil idea is interesting. I did hear some minor backfiring after it quit and I tried to restart it. Not sure how you test a coil.

Thanks for the ideas.

Found a rebuild kit for your motor at $33 and $66 bucks thought is worth sharing the link.


https://www.amazon.com/dp/B0781FFW4...&pd_rd_r=b5a79e26-0f1d-11e9-9319-5d317ee48912
https://www.everestpartssupplies.co...buretor-ignition-coil-recoil-muffler-and-more

 

[North Idaho Wolfman]

Eldubya, yup I agree with what your saying - that's the mystery - the new plug seems to have fixed the issue and I just don't understand how that could be.

One thing I have discovered is that when the resistance on the plug gets too high it will overheat the coil and it will stop sparking, let it cool and tada it runs again.

 

[William1]

One thing I have discovered is that when the resistance on the plug gets too high it will overheat the coil and it will stop sparking, let it cool and tada it runs again.

Exactly.

OEM plug is a resistor plug. Inside, the voltage from the spark plug cap enters the connection on top. Inside the ceramic, is a length of resistor carbon. Then another length of metal rod that terminates as the center electrode. The carbon resistors crack or disintegrate. The moment load is applied, the rush of heat causes them to fail. The engine might start fine and run at full rpm with no load.
Insidious!
I replace the plugs with non-resistor ones. Resistor plugs are only to comply with radio interference regulations and not a issue for 99.9999% of the people.

 

[AndyM]

KennysNewFarm - that kit looks great thanks for the lead.

NIW - THAT sounds like whats going on. I looked closer at the plug and there are no cracks or other signs of were. Gap was right on spec. But high resistance is not something I can see (Is it testable?)

William1 - Sounds like we have an answer - it WAS a resistor plug.

Thanks to all - makes sense now!