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Old 03-15-2010, 11:35 AM   #1 (permalink)
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87 Octane or 91 Octane for my Dyna?

When I bought my 1995 FXDL a few months ago, the previous owner said to use only 91 Octane fuel. However, I just bought a service manual for my bike, and it says to use 87 octane or higher. I'm wondering if there is something that I'm missing. Can I use 87 octane? Looks like I can.
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Old 03-15-2010, 11:59 AM   #2 (permalink)
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Originally Posted by jcbii View Post
When I bought my 1995 FXDL a few months ago, the previous owner said to use only 91 Octane fuel. However, I just bought a service manual for my bike, and it says to use 87 octane or higher. I'm wondering if there is something that I'm missing. Can I use 87 octane? Looks like I can.
I've got a 98 FXD and I run premium. I've run 87 in it now and then when that is all that's available and it runs ok, but you may get some minor spark knock. I don't like any spark knock so I run the 91. You can also slightly retard the timing if you get minor spark knock and still want to run the 87.

Last edited by rickr01; 03-15-2010 at 12:01 PM.
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Old 03-15-2010, 12:05 PM   #3 (permalink)
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Originally Posted by jcbii View Post
When I bought my 1995 FXDL a few months ago, the previous owner said to use only 91 Octane fuel. However, I just bought a service manual for my bike, and it says to use 87 octane or higher. I'm wondering if there is something that I'm missing. Can I use 87 octane? Looks like I can.
Did the previous owner make any engine modifications?

Some modifications (e.g. increased compression) may necessitate higher octane fuel.

If no engine mods, then I would go with the Owner's Manual recommendation. However, if I recall correctly my 1984 Evo required premium gas. I know I ran premium in my 1995 FLT but I don't have the Owner's Manual available to me now to confirm it was required.

Over 12,000 miles, at 45mpg, you will use about 270 gallons of gas - at $0.25 per gallon difference that is less than $70. I would just run premium and not worry about it.


You don't say if your service manual is a GENUINE Harley-Davidson Service Manual SPECIFIC for your year and model. If it is, then that information would be correct.
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Old 03-15-2010, 12:18 PM   #4 (permalink)
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Did the previous owner make any engine modifications?

Some modifications (e.g. increased compression) may necessitate higher octane fuel.

If no engine mods, then I would go with the Owner's Manual recommendation. However, if I recall correctly my 1984 Evo required premium gas. I know I ran premium in my 1995 FLT but I don't have the Owner's Manual available to me now to confirm it was required.

Over 12,000 miles, at 45mpg, you will use about 270 gallons of gas - at $0.25 per gallon difference that is less than $70. I would just run premium and not worry about it.


You don't say if your service manual is a GENUINE Harley-Davidson Service Manual SPECIFIC for your year and model. If it is, then that information would be correct.
The previous owner said he bought it new with the Screamin Eagle pipes (which I removed to put stock pipes back on). He didn't know if they did anything else, so I'm assuming no engine mods were done.

As for the difference, I guess you're right in that it doesn't matter that much regarding $$. But I also wondered if running 87 octane would do any damage.

The service manual is geniune Harley-Davidson. I bought it from a Harley Davidson dealer, and it cost me $70 (ouch!), so I hope it's authentic. On page 1-9, it says 87 octane or better and then refers the reader to Section 3 - which basically says the same thing, but provides more information regarding the types of fuel (methanol, ethanol, etc.).
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Old 03-15-2010, 05:48 PM   #5 (permalink)
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The previous owner said he bought it new with the Screamin Eagle pipes (which I removed to put stock pipes back on). He didn't know if they did anything else, so I'm assuming no engine mods were done.

As for the difference, I guess you're right in that it doesn't matter that much regarding $$. But I also wondered if running 87 octane would do any damage.

The service manual is geniune Harley-Davidson. I bought it from a Harley Davidson dealer, and it cost me $70 (ouch!), so I hope it's authentic. On page 1-9, it says 87 octane or better and then refers the reader to Section 3 - which basically says the same thing, but provides more information regarding the types of fuel (methanol, ethanol, etc.).
If you are not hearing spark knock you are not damaging the engine with the 87. You will run into some areas that only have 87. It's fine to run in a properly tuned motorcycle.
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Old 03-16-2010, 12:51 AM   #6 (permalink)
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If you are not hearing spark knock you are not damaging the engine with the 87. You will run into some areas that only have 87. It's fine to run in a properly tuned motorcycle.
What's spark knock? I'm hearing (and feeling) some sputtering when I accelerate. Is that what you're talking about?
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Old 03-16-2010, 02:13 AM   #7 (permalink)
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I have the 2009 owner's manual from Harley and they specify 91 octane fuel.

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Old 03-16-2010, 09:02 AM   #8 (permalink)
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What's spark knock? I'm hearing (and feeling) some sputtering when I accelerate. Is that what you're talking about?
Spark knock (some describe it as pinging or detonation) is a metalic sounding rattle that occurs when accelerating mostly under load. Advanced timing and lower than recommeded fuel octane can cause spark knock, but obviously there are others. Under very heavy acceleration a little minor pinging for a second or two is not anything to be concerned about but constant Spark Knock which sounds like someone is in the engine throwing marbles around is not a good thing. In a fairly stock or lightly modified engine, (not a high compression engine) it is normal to hear a little spark knock under heavy acceleration when using lower octane fuels. Retarding the timing just slightly will take care of this but you will suffer a little loss in the seat of the pants acceleration feel. Rather than play the game or take the chances, I would just run the 91 octane. If she runs good on 91 with no noticable spark knock then all is well!
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Old 03-16-2010, 10:27 AM   #9 (permalink)
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Greetings,
With all the ethanol showing up at the pump, I would run premium.
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Old 03-17-2010, 12:36 AM   #10 (permalink)
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Originally Posted by rickr01 View Post
Spark knock (some describe it as pinging or detonation) is a metalic sounding rattle that occurs when accelerating mostly under load. Advanced timing and lower than recommeded fuel octane can cause spark knock, but obviously there are others. Under very heavy acceleration a little minor pinging for a second or two is not anything to be concerned about but constant Spark Knock which sounds like someone is in the engine throwing marbles around is not a good thing. In a fairly stock or lightly modified engine, (not a high compression engine) it is normal to hear a little spark knock under heavy acceleration when using lower octane fuels. Retarding the timing just slightly will take care of this but you will suffer a little loss in the seat of the pants acceleration feel. Rather than play the game or take the chances, I would just run the 91 octane. If she runs good on 91 with no noticable spark knock then all is well!
Thanks for the info. I don't hear any pinging when accelerating, but it sputters some. I just had it tuned by a local shop, but I'm not really confident they did a good job. Anyway, I guess that's another story. As for spark knock, it sounds like I don't have that. I do hear some pinging when it's just sitting and idling, but I figured that was a pushrod or valve making that noise. I'm coming off a Suzuki, so I'm sure some of these noises will just sound strange to me for awhile.
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Old 03-17-2010, 12:42 AM   #11 (permalink)
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With all the ethanol showing up at the pump, I would run premium.
I try to run Chevron premium when I get the chance. But in all honesty, I can't really tell the difference in how the bike runs when I use 87 octane or 91. But I have to admit I've filled it with 87 octane when the tank was probably half full with 91 octane, so I don't have any real comparisons to make any conclusions. I was just surprised by my service manual said 87 octane.
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Old 03-17-2010, 10:13 AM   #12 (permalink)
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What is the difference in price? 35 cents a gallon?

So for a buck and a half (on a tank full) you are going to take chances?

Doesn't make any sense to me at all. I run best I can get in my 97 Dyna. If they have 92 thats what goes in.
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Old 03-17-2010, 10:52 AM   #13 (permalink)
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What is the difference in price? 35 cents a gallon?

So for a buck and a half (on a tank full) you are going to take chances?

Doesn't make any sense to me at all. I run best I can get in my 97 Dyna. If they have 92 thats what goes in.

. Very good point!
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Old 03-17-2010, 02:36 PM   #14 (permalink)
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. Very good point!
I'm sold on using 91 octane, and that's what I plan to do from this point on. Just thinking about it, my manual (page 1-9) says "Usa a good quality leaded or unleaded gasoline (87 pump octane or higher)." What this probably means is that 87 would be the minimum, but use higher if available. At least that's what I'm going to assume.

But just for the sake of discussion - Let's say the manual said "Use 87 octane only". Is there a risk of causing performance problems or damage by using a higher octane? I was told many years ago that higher octane gas is not "better" gas, it just burns slower so there's no pinging or pre-detonation in high compression engines. So what would the effect be of using higher octane in a stock engine where the detonation is slower than what the engine was designed for?
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Old 03-21-2010, 10:47 AM   #15 (permalink)
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I'm sold on using 91 octane, and that's what I plan to do from this point on. Just thinking about it, my manual (page 1-9) says "Usa a good quality leaded or unleaded gasoline (87 pump octane or higher)." What this probably means is that 87 would be the minimum, but use higher if available. At least that's what I'm going to assume.

But just for the sake of discussion - Let's say the manual said "Use 87 octane only". Is there a risk of causing performance problems or damage by using a higher octane? I was told many years ago that higher octane gas is not "better" gas, it just burns slower so there's no pinging or pre-detonation in high compression engines. So what would the effect be of using higher octane in a stock engine where the detonation is slower than what the engine was designed for?

NO EFFECT, NOTHING, NADDA! Stop worrying, put in gas and enjoy the ride.
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