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J

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So i was out riding last week and my bike started making a racket. After getting the old girl up to the shop the engine was droped and Clayton opened her up. I got a tank of bad gas from some cheapy gas station i stopped at after my fuel light came on. With the high compression i was running and the bad gas the engine was detonating early. The result is a week of not being able to ride and some messed up piston skirts and some cylinder damage. /Shrug..

If you are running higher compression i strongly recommend that not only you get the highest octane available but also only go to the bigger named and more frequently visited gas stations.

As for me my bike comes back from the dyno tomorrow with some new mods thrown in. ;) I cant wait.
 

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I was going to offer to pull your finger, but I see you have things well under control... :p


Thanks for the heads up. When you say bad, do you mean improper octane or old fuel?
 
J

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I would say low octane. My compression wasn't all that high and shouldn't have early detonated with the 91-93 (depends on gas station) octane i use.
 

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Hmmm. Is that what you would normally expect with lower octane fuel in your rig? I'm a blatant non-gearhead and pretty much a neophyte when it comes to compression and octane...
 

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The most important tip in buying gas is to go to stations that have a lot of traffic. Gas doesn't age well. If you are running a modified engine that needs premium and you go to a station with little traffic then the premium you pump could have deteriorated. The combination of little traffic and lower premium sales can result in very bad premium at the pump. When premium ages its octane rating falls dramatically. If you run regular in a stock engine the same thing can happen.

Buy fresh gas of the octane you need.
 

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andyauger-- Can you expand on what you mean when you say fuel doesn't age well? How does aging of gas affect the octane rating? Is there anything other than octane lowering that becomes a problem such as settling out (stratification/layering), varnish/carbon separation, etc? Thanks...
 

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All gasolines are blends of various hydrocarbons with a variety of additives. In any tank, whether on the bike or in the ground, the lighter ends evaporate first. Lighter ends tend to raise octane rating, so as they flash off the octane rating falls. Some additives and some hydrocarbons will solidify and settle out. The varnish you see in old carbs is actually very heavy hydrocarbons that have accumulated after years of running. Same with that orange, powdery stuff. This is a simplified version of the process, but you get the idea.

It gets pretty complex chemically, the process isnt' uniform and varies with the particular blend. For example, depending on the blend, you could wind up with lower octane and harder to ignite fuel (remember that one of the reasons to use high octane is to resist early combustion).

Blends are adjusted by season. Summer blends generally last longer than winter blends. Winter blends have very light ends to enhance cold start vaporization. If those blends warm up those light ends go away quickly. So summer blends sitting around in October may be fine while winter blends sitting around in May could be really bad. As you might imagine, winter blends in Louisiana and Minnesota are not alike.
 

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andyauger-- Ahh, now I get it. Thank you!!
 
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