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What octane grade should I use?

902 Views 7 Replies 4 Participants Last post by  hogcowboy
I ride a 1980 suzuki gn400.. What grade of octane should I use??
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Most Suzuki bikes use 87, except for the high compression ones (greater than 10:1). If you can find out the compression ratio, you will find your answer. Another reason for using higher octane is if, when fully warmed on a hot day, you crank the throttle and hear pinging/knock, go up a grade.
The compression is 9.2:1 so 87 will do just fine?
Even though I get an argument sometimes when I say this, I gotta say it.
The owners manual will usually state the Lowest Octane the manufacturer can get away with recommending.
I believe it to be a sells tactic. (I'll buy X bike so I can use the low octane fuel, says so in the book).

If you know what to look for you can see improper octane when studying the condition of the spark plugs that have run in a properly maintained machine.
I've seen the spark plugs disagree with the book several times, especially in big twin engines.
Will it be enough to kill the engine? Probably not but why overwork it for a few pennies per gallon...
The compression is 9.2:1 so 87 will do just fine?
Yep, 87 should be okay for that machine.
Awesome, thanks for the feedback!
It will probably run best on 87. Octane ratings are a measure of how hard it is to ignite the gasoline, with the higher number meaning harder to ignite. That's all. Higher octane gas usually needs higher compression to burn properly, and it burns more slowly under lower pressures, meaning it is likely a higher octane gas will finish burning in the headers, instead of the cylinders, in your bike.
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You might also download a pdf of the owners manual if you don't have one already and
. :grin:

Owners manual 1980 Suzuki GN400 pdf
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