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Discussion Starter · #1 · (Edited)
About 45 years ago I discovered a brand new Champion resistor spark plug that wouldn't fire. I broke it apart and found its resistor was missing. A manufacturing defect. Now fast foreword 45 years to the present day and I discovered another Champion spark plug that was barely firing. I live off the grid on generator power and my large 9000 watt Honda V-twin generator engine recently began misfiring. I found the 1/4" fuel hose leaving the tank was almost completely plugged so I blew it out, thoroughly blew out the 5 gallon tank, and installed a new fuel filter but my engine still misfired. I checked its two Champion #3405 platinum spark plugs and found one was completely fouled with black soot and gasoline. I sand blasted them and put them back in but my engine still misfired and I once again found one spark plug was fouled with black soot and gasoline. Perhaps a bad coil? As this engine has MANY hours on it I replaced the two coils (only $15 for the pair) and it still misfired.

I checked its compression and found it had 105 psi and 110 psi which is normal for a "pull start" small engine with an automatic compression release (it's built into the camshaft). Then I discovered its carburetor was internally plugged and I wasn't able to completely take it apart to remove the plug so I bought a new replacement carburetor for $25, installed it, and it STILL misfired. What the heck is going on? During my spark plug cleaning and reinstalling I happened to notice one spark plug fouled regardless of which head it was in and that's when I suspected that one spark plug was defective. Even though it looked perfect on its outside perhaps its resistor had burned up. I put two new DENSO iridium spark plugs in it and away it went.

Champion used to make "spark plug testers" that consisted of a rectangular steel box that had a place to screw a spark plug into, a glass viewing window, an electrical cord, and a place to attach an air hose. You could turn it on and view the tip of the spark plug firing through the glass window. As you turned a knob that increased air pressure in the box you could watch the spark plug QUIT firing as the pressure increased. At ambient pressure a spark plug will easily fire BUT as the air pressure increases there will be a time in which the spark can no longer jump the gap. The spark plug testers were commonly seen in dealerships and auto repair shops back in the 50's and 60's but I haven't seen any since then.

The lesson learned? Spark plugs can appear perfectly normal on their outside but fail to fire under compression pressures. Are Champion spark plugs inherently defective? Poor quality materials used in their construction? Just a coincidence that TWO Champion spark plugs failed to fire? The jury is out..............
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