Plugs #1 and #4 more fouled

[dbuelke]

Notoriously these two plugs show more fouling while #2 and #3 will appear clean. I understand this is due to the fact the two end cylinders run cooler because of their 3-side exposure, while the center ones run hotter because more heat builds up between those two cylinders as a result of their confined proximity. Would there be any advantage to setting the gap on the two pairs of plugs differently to try to get two cylinders to run cooler or two to run hotter? How about using different plugs with different heat ratings?

[Norman Kling]

I would think this would happen more often if you run a water pump because it recirculates the cooled water faster than the thermosyphon system. If you have a water pump try removing it and running just a fitting like Henry did. Also try leaning the mixture just a little. Rich for starting but leaner when warmed up. Usually the fouling is caused by too rich a mixture.
Norm

[John.Zibell]

I don't what to start a big discussion, but I run a 160 degree thermostat in my thermosyphon system. All plugs run the same color with no fowling. Also using an IR thermometer, the head temperature has practically no variation from rear to front.