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Well, the bike is tuned for 87 octane, and it runs well. If you use 91 or better, it really won't go any faster, just that the engine will run cleaner, and possibly smoother. If you want more performance, then you would have to adjust the timing. BUT, with the price of fuel, and if you drive a lot, better just to leave it as is. A tank here or there of 91 is good to do though.

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โˆ™ 2008-08-18 00:08:22
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Q: What will 91 octane do for my 1983 650 hawk that 87 can't?
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