Quote:
Originally Posted by superjocko
... If the mixture is in the 13-ish : 1 ratio at WOT, I still wouldn't expect much additional coloration of the plug insulator on a short plug reading run. 13:1 is still fairly lean for a maximum power scenario unless the engine in question is in a relatively mild state of tune mechanically (compression, cam, etc.). Air fuel ratios of 10.5:1 - 12.5:1 are generally considered safer for maximum load conditions on an engine that may be approaching conditions of pre-ignition under high load demand.
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Having run a few miles wide-open (in both 4th & 5th gears), cut ignition (withOUT closing the throttle), pulled the spark plug and examined the plug insulator, it would take a vivid imagination to detect a color difference.
vs. part-throttle at 5,000 rpm
My vivid imagination detected VERY slight greyish coloring vs. the snow-white insulator at 5,000 rpm partial throttle.
This Grom engine is a 'mild tune' ... SOHC, 2-valves, 10:1 compression, running 87 octane. At wide-open throttle for miles, the instrument panel indicated 102 mpg, btw ... ` gotta make ya smile! ... even though it'll only transport you at 45 - 50 mph, sitting straight up (no tuck) on a flat road sans much wind; ` amazing what 8.7 hp to the wheel (per dyno) will do for ya !
Why point out this non-China-bike example? I did so as an illustration of what spark plug insulators might look like, managed by
a current ECU injection system.