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: