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I have a 74 Honda XL125 that eats spark plugs. I've had exactly the same problem on a 69 Honda 750. Both could be running great one day, then the next day wouldn't start. Remove the plug and check for nice hot spark--looks great. But, the engine will not fire. Put in a new plug, starts right up. I go through a plug every month or two.
Any idea what's wrong? How can a plug look like its firing great and still won't start the engine? What's making the plug burn out or whatever is happening to it?
By the way, I've seen this same question on a hondabike.com website, but they wouldn't let me register because I have a Yahoo address. Huh?
Royo

Could it be a weak coil or the wires are failing? that is where I would start. The next time you have a no start, wiggle the spark plug wires around. If it then starts i'd change em out. As for testing the coil...I do not know what the proper resistance should be. Maybe your manual will tell you. If this doesn't help i'm sure there will be someone else on this forum that will know more than I.