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Well, Craig, I'm sure that most of us come to conclusions based on experience. And often, this experience is reinforced by others so it kind of becomes accepted knowledge. My training at the university was that once a plug fires, it can't do anything to improve combustion. So a small spark that is absolutely reliable every time (100% firing) provides the same result as a large spark that is 100% reliable. That information was backed up by lab tests. A quite a few people will disagree with this. Different heat range plugs are designed to help with fouling. The obvious question is "Why not put the hottest plug in everything?" And the answer is "Because the hotter plugs run hotter and age (burned electrodes) more rapidly." So you use the coolest plug that the tractor will permit - without fouling. And your last question is about Champion plugs. Quite frankly, this one is still a mystery to me. I'll relate my experience - many have already seen this - sorry to repeat it if you have. I rebuilt a WD Allis. I bought a different block, put in M&W cylinders and pistons, and new rings. Valves were good so I just lapped them in. I did a full tune up with brand new Champion plugs. I started her up and she initially had a fairly consistent miss-fire. It wasn't a typical misfire as the cylinder miss-firing moved around. I determined this by removing one plug wire at a time. Oddly, it ran exactly the same way each time - regardless of which plug wire was removed, the miss continued. So I pulled the intake off and put in my mill and re-machined it flat. No difference. I pulled the valve cover and checked the clearance of every valve. No difference. I checked the timing. No difference. I checked the fuel flow. No difference. Finally, I pulled the new Champion spark plugs out and replaced them with the old AC plugs that were in it when I pulled the engine apart. I started her up and WALLA!!! It ran perfect - never a mis-fire. I took those same Champion plugs and put them in my Ford 8N and they worked fine - an occasional misfire but very occasional. I then checked this board and discovered a number of folks who had the same experience. That convinced me that I hadn't had a supernatural experience. I use AC or Autolight now on all Allis tractors. I don't buy Champion on purpose anymore.
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