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Motorized Bicycle General Discussion All topics regarding bicycles with engines.

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Old 05-02-2009, 12:41 PM
marioaz marioaz is offline
Motorized Bicycle Senior Member
Join Date: Dec 2008
Location: Prescott, Arizona
Posts: 65
Default Octane Question

Breaking in a new GT-4. NGK B6HS. Smaller plug gap, .020-.025 had the top end clanging and rattling. Predetonation? Re-gapped to .030 to retard the timing, and most of metallic rattling has ceased but bike a little slower on run up. Using Shell 87 octane. Does higher octane affect these engines as far as predetonation goes?
Grubee instructions plug gap is .036?
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Old 05-02-2009, 04:14 PM
Bikeguy Joe Bikeguy Joe is offline
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Join Date: Jan 2008
Location: up north now
Posts: 11,531
Default Re: Octane Question

Octane will have little to no effect on these. They have around 6.5 to 1 compression. I would look to the wrist pin for the clatter.
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