Octane rating - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 17 (permalink) Old 07-02-2014, 10:03 AM Thread Starter
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Octane rating

Just wondering which is the best fuel to run in my 05 1100? I do experience a backfire from time to time when i crack the throttle while say setting at a stoplight getting ready to take off. I normally run mid-grade 89 octane...any suggestions?

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post #2 of 17 (permalink) Old 07-02-2014, 10:53 AM
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Yamaha recommends 87 octane for that bike. The only reason you would need to go above that is if you are experiencing knocking. The occasional "backfire" you're hearing is because you're dumping extra fuel onto the fire without providing the airflow required to properly burn it, since you're sitting at a stop light when you crack the throttle.

Placebo effect is powerful on the mind, but running a higher octane rating will not improve your bike's performance if you're not experiencing knocking. The claims of additives to clean your fuel system are hype too. That stuff doesn't exist in the fuels at a concentration required to have an impact. Run some SeaFoam if that's what you're looking for.

It also should have no impact on your average mpg. I see better mpg on the rare occasion that I stumble onto fuel without ethanol, but that's harder to find in my area nowadays. I recommend you just run 87 octane in that bike...and so does Yamaha.

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post #3 of 17 (permalink) Old 07-02-2014, 10:55 AM
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The manual says to run 87 and I have never had a problem with it. Search the fuel threads... this subject gets rehashed pretty regularly

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post #4 of 17 (permalink) Old 07-02-2014, 11:44 AM
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The fuel isn't likely to be problem. It is likely a little running rich at idle and unburned fuel is accumulating in the exhaust.

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post #5 of 17 (permalink) Old 07-02-2014, 11:46 AM
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Lucky us the lowest rating is 95 super is 97.
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post #6 of 17 (permalink) Old 07-02-2014, 03:14 PM
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The backfiring may actually be a lean condition. What pipes? What intake? Jetted?

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post #7 of 17 (permalink) Old 07-02-2014, 03:50 PM
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Quote:
Originally Posted by rmccutchan View Post
The backfiring may actually be a lean condition. What pipes? What intake? Jetted?

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Agree.

Afterfire is typically what most lay people call a backfire (albeit technically incorrectly so). This is the explosive burning of fuel in the exhaust.

Backfire is ignition on the intake side that can be caused by a lean mixture among other things.

Fuel mixture, operating temperature of the engine, operating temperature of the exhaust, ignition timing and valve adjustment all can be part of the cause of the popping noise.

Examining the fuel mixture issue is the simplest place to start. I still suspect a rich mixture.

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post #8 of 17 (permalink) Old 07-02-2014, 07:32 PM
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Quote:
Originally Posted by Slayer View Post
Agree.

Afterfire is typically what most lay people call a backfire (albeit technically incorrectly so). This is the explosive burning of fuel in the exhaust.

Backfire is ignition on the intake side that can be caused by a lean mixture among other things.
it fires in the back of the bike. i'm calling it backfire.

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post #9 of 17 (permalink) Old 07-02-2014, 08:21 PM
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Quote:
Originally Posted by bevo1981 View Post
it fires in the back of the bike. i'm calling it backfire.
And the great majority of people will understand exactly what you mean.

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post #10 of 17 (permalink) Old 07-03-2014, 07:49 AM
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Backfire on decel in the exhaust is caused by a lean condition at idle. There isn't enough fuel in the mixture to fire the cylinder every time....which dumps some unburned fuel into the pipes. Then when the cylinder does finally fire, it will ignite the unburned fuel when the exhaust valve opens. It's most noticeable with aftermarket pipes which allow more air to flow...but does happen a little with stock mufflers as well.

To fix it, you just need to turn the Pilot Mixture Screws out 1/8 to 1/4 turn. That'll enrich the idle mixture and stop the backfire.

Here is the same info direct from the Mikuni tuning guide....they probably explain it a little better

http://www.mikuni.com/fs-tuning_guide.html

and to answer your question about octane and backfire......they would have very little to do with one another.

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Last edited by Sick Mick; 07-03-2014 at 07:52 AM.
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