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Discussion Starter #1
Hey guys, I've been reading FAQs and other articles noting to use lower octane gas (87) in our V-Stars due to the lower compression of the engines and to reduce popping/backfiring. I'm just curious as to why this is. Isn't a higher octane gas more resistant to combustion? Just curious as to why the lower octane is better and what people have experienced.
 

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The higher the Octane number the more resistance there is to pressure induced ignition. You're right that it is not necessary with these fairly low compression engines. The slower burning fuel, high octane, lends better lends itself to collecting in the exhaust. When you back off throttle you close off the fuel, this creates a lean condition which can fire not at all or sporadically late which then ignites thie collected fuel. Mikuni says this is a normal condition... However it is aided by the introduction of fresh air, can you say AIS. An occaisional pop is OK. Use the 87 with confidence, but I always try to stay away from the cheap stuff and get a Top Tier Gas.
 

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Yes, higher octane is more resistant to combustion. It is used for higher compression engines such as on sport bikes and sports cars, where more pre-detonation (pinging) can occur due to the higher compression of the fuel/air mixture taking place, which causes the hotter vapor to combust before the spark plug can ignite it. The higher octane helps stabilize this combustion to reduce pre-detonation.

So, it's not so much that the lower octane would be better for the lower compression engines, it's that the higher octane is not necessary and would provide no benefit.

One thing I noticed when trying higher octane on my bike a while back, was that in cold weather, the bike was harder to start using higher octane than with the lower octane.

As long your bike doesn't ping using the lower octane, the low octane should be perfectly fine.
 

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Discussion Starter #4
Thanks guys - Just like to why certain things are ;)
 

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this is the first Yamaha ive ever owned,,, i always run a higher octane. the main reason is when you tear down your engine or even your carbs, you wont have the carbon build up that you will get with the cheaper gas. From a person that has worked on his own stuff(junk) all his life, if your fuel system is clean, carbs heads cylinder walls and pistons the easier it is to troubleshoot problems on the internal areas.. Happy riding & keep the rubber side down!
 
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