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Old 04-10-2011, 07:47 AM
Nougat Nougat is offline
Motorized Bicycle Elite Member
Join Date: Nov 2009
Location: Montgomery, IL
Posts: 1,332
Default Re: sparkplug gap size

For the record, I had mine (B6HS in a 50cc HT) gapped at .032 and it ran pretty well. Then I added an SBP pipe kit, a hi-flow air cleaner, and it ran ... differently. Hard to start, low power. It was now a "Morose Time" engine.

I decided to put the gap back to .026, and it perked right up. Night and day, I tell you. I didn't expect it, either, but there it is.

The thing to know about spark plug gapping is that a narrower gap makes it easier for the plug to spark (less resistance), but generates a smaller spark. A wider gap is harder to spark, but generates a bigger spark. What you want is a balance of the two; a gap wide enough that you get the fattest spark that the CDI is able to consistently generate. There's also a theory that a smaller gap allows the plug to spark just a bit earlier, and a larger gap allows it to spark just a bit later, which would have a teeny tiny effect on ignition timing, but I don't know that anyone has looked into that at all.
When asking for advice, you did not specify whether you wanted only good advice.

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