Kohler M20 spark plugs
 

Just thought I would share some information about the Kohler Magnum 20 , I was doing some regular maintenance and decided to try the Autolite xp 26 spark plug. I can say without a doubt the engine runs a lot better in a noticeable way such as easy starting and throttle response also seems to have or hold the governor when you really put a load on it. So I thought I would try a new set of the champions rv17yc it definitely runs better with the Autolite xp, I hope this helps someone.

It's in your head. I assure you.
Iridium basically handles high energy spark better, and thus lasts longer. The small magneto in your M20 doesn't make a hot enough spark to see an advantage of a $7 spark plug.

Pretty basic spark plug rule says use what the manufacturer recommends. Kohler says use a copper plug.

This is really more of a question than a comment. I'm no spark plug expert. I know what to put in what engine and why... With that said I have never tested or studied or compared one against the other.

If an iridium plug handles high energy better, could that mean that its also more efficient with a lower energy spark? I thought as plugs progressed and matured from plain ole copper to what we have today the whole idea was to be more efficient. I'm not saying you will see a noticeable difference in running necessarily especially across just 1 or 2 cylinders but do you think they would be somewhat more efficient?

Been my experience that spark plugs spark.
Only times I saw a difference was when the wrong heat range was used and either they fouled, or burned a window in a piston.
But even at that, most times it really was not the plug that was the problem.
The best preforming plugs were always the ones on sale. :biggrin2:

I agree. It's hard in most standard applications to put in a plug that makes a vast improvement. Definitely not a power improvement. Maybe take away a cylinder knock. However, with the increased voltage (which also made for a much larger plug gap because the flame could actually jump the distance) the need for a plug that would not burn up because necessary. Also, a lot of ignition systems went back to wasted spark (for emission reasons) and that caused the need for double (platinum/iridium) tipped plugs. So.... in those applications there is a need for the "high end" spark plug. But in an old point or mag system, they are just a waste of money.

I'm also a bit worried they may create a flame that will burn a piston. The design of of a plug creates a consistent burn. A "better" spark may ignite the fuel too quickly and while it may appear to give a power increase, it's detrimental to the life of the engine.

I'm kind of thinking this through as I post trying to come up with a good answer as to why it appears to give a power increase, and why that isn't necessarily a good thing.

From what I am reading online. Its not a good thing for these smaller engines. People have described exactly what your talking about. The iridium plugs have a much smaller electrode and wire. I am reading and it makes sense that the smaller tip "electrode" requires less energy to achieve the same spark or better. With this better spark people are getting some degree of pre ignition and while it appears to give some more power it is usually short lived. There were other tales of problems when running them for extended periods.

I would post findings here but i looked at about a dozed sites and all said close to the same thing.

I’m only telling you guys about my experience with the 2 differences. The engine had regular Autolite 26 in it, im not saying that it ran bad but I just wanted to try something else, and it started a lot better with the xp plug VS new champions, I’m not trying to start a debate about waisting money or arguing about it, just saying it works for me, if I can get time to do a video I will so I might be asking how to post a video.

I think you are missing the point bud. It doesn't matter what worked "for you". An iridium plug is detrimental to the engine. It causes hot spots and you will burn up your pistons. But hey, if you are OK with a short engine life, then by all means, be our guest and keep them in.

I'm thinking an old flathead ain't going to be too sensitive to a little timing advance or pre-ignition @ 6.5 to 1 CR.
But I haven't done any scientific work to that fact.

Now take a SBC of the 60's vintage with 10.25 CR and cheap gas, will take the heads off the pistons in a heartbeat.
BTDT and it wasn't pretty. :biggrin2:

Jonathan where did you get that scientific information about the plug? I would like to look that up and read about it, just curious about it

I have never had good luck with Champion plugs dating back to the 60's. I like NGK or Autolite. :beerchug:

I really don't know George.... The old K motors were bad about burn pistons, just from normal use and wear, let along when they weren't tuned right. I've tore them down with few hours on them, most everything looking good, and not much machining needed, but the piston was melted to the top ring on the plug/valve side. And I've seen them with little wear and a blue million hours on them. The KT's and Mag's didn't seem to have the same issue even thought they are basically the same design. Difference being spark plug location and head chamber shape. Does make one wonder if the plug coming into the side of the head up above the valves made for a better burn. Seems the valves wear out and fail in the KT's and Mags more often though, so there is always a trade off to a different design. I agree, lower compression and the engine design may take the increase in timing (assuming the plug actually does fire enough sooner to matter) along with some pre ignition and be ok. I still wouldn't risk it..... but I'm also just not going to pay more than $3 for a spark plug for my "lawn mower" when a copper resistor works so well. I haven't even changed the plugs in any of mine in I couldn't tell you how long. 1811 is due.... but it needs more than plugs. I just rolled 2100 hours on that tractor, and this engine was installed at 1175, so I need to pull the heads and check things out.


I didn't present any "scientific" information. Mostly experience, and knowledge from years of service. Oh, I read some stuff since this posting.... because I'm to the point now I'm starting to forget things that are kind of trivial. Google it. Info is out there. Just watch who and where you get your info from. On the internet, you can literally find people on both sides of the fence. Easy for me to spot the BS.... but if you don't know and understand some stuff, then sometimes you can be fooled. Likely how you came to purchase the plugs in the first place. Sorry if that offends.


This statement always puzzles me. Kind of like the whole ethanol debate. A lot of people say they have issues with Champ plugs. Most of them people I have a good deal of respect for. (You and Dale Merkle come to mind.) I've never had bad luck with them, except on rare occasion. I've always ran them in the Cubs, and put them in every Mopar engine that I ran through the shop with no issues. I usually chose Champs for the old tractors I used to overhaul too. I often wonder if it's a fuel related issue. I've never had issues with ethanol, matter of fact I have good results with ethanol. But others swear to the end of the earth that ethanol caused them all kinds of issues. Wonder if it's luck of the draw... or fuel... or ???? I'll keep using them until I have an issue. Biggest issue I have with Autolite plugs is that's what Ford runs, and I just can't stand the thought of using a "Ford" spark plug in anything I own. :biggrin2::biggrin2::biggrin2: NGK is a great plug and my next choice when I can't get a Champ or an AC Delco. (As a note, I stick to what OEM was on most everything, so like my Chevy truck gets AC Delco plugs.)

Per the recommendations of the majority on this site, I switched from the original Champion plugs to the Autolite 26 plugs. Both of my Magnums run better and start better now. I set the gap to .025".