I run 91 because that's the highest they seem to sell in the Bay area.

Must be OK because there arent any pings.

i have been looking for any un-mixed fuels here in texas, no luck, i add octane boost to help kill the pre ignition

Always use premuim Sunoco 93 when I can

Octane is a retarder as previously mentioned. High compression and high heat will cause the fuel to ignite prematurely, putting extreme stres on the engine by exploding while the piston is still compressing. When my bike was an 883, I used 87 and it ran fine. Now after the 1200 conversion and high compression mods, 87 will sound like a drum solo on a tin cup. Octane keeps the fuel stable until it gets ignited by the extreme high heat of the arc on the sparkplug instead of the moderately (in comparison) high heat of the cylinder walls and lowering of the fuels flashpoint via high compression.

This is why diesel fuel is used in diesel engines, it resists ignition well past the compression generated by a gasoline engine and then is ignited by pressure alone. you could never get to full operating pressure with gas in a diesel because it would ignite way too early. This high compression is why diesels have so much torque at low RPM.

Bottom line, if it's not pinging, you don't need higher octane. If it's pinging....you do

Almostforgot.....most of the carbon build up is from running too rich a mixture. you can drill out the EPA plug on carbs and adjust the idle mixture screw (it's a crime LOL) to lean it up a bit. you can also rejet the carb. The idle mixture screw (Not the idle speed setting screw) and jets control fuel flow at different rpm's. My Sporty has Keihnin CV for instance. It's got the Idl mix screw, a slow jet and a fast jet. Obviously the idle mixture is for idle fuel supply only, then mid range is suplied fuel by the idle mixture orifice and the slow jet orifice, then high range throttling uses the fast jet/slowjet/idle jet to supply fuel. So each jet has a range it kicks in and is then in use until you come back down below it's range of use. with an air/fuel meter, you have to inspect the plugs. this is a seat of the pants art form and I can't write a book here but, broken down, if your plugs are clean or have ligt brown to white soot on them; your too lean and need to increase (enrichen) your air/fuel mixture. Black soot is too rich (if it's on the plugs, it's on everything else too). You should be looking for a medium brown residue on the plug. Keep in mind, you may have the correct idle mixture settingand slow jet sooting that may be masking a fast jet lean problem as the high rpm dwell time may not b enough to burn off the correct brown soot from the lower ranges to reveal the too lean condition off the fast jet. It takes a lot of plug cleaning and re-running to get it dialed in. there will be times i will take a clean set of plugs in my pocket out to a country road, install them and immediately go balls to the wall to soot them up and then kill the engine before stopping so i don't screw up the fast jet sooting so i can see what i'm getting at high throttle settings without the idleand slow jets leaving their mark on the test plugs.....Did i mentin i get a little OCD about some things.

I have always just used what the manufacturer has called for. Never have I had a fuel related problem in either auto or motor. Currently...since 1984, last Harley...use 87. The last time I saw Ethyl was when I was putting around in a 67 Goat, I do miss the both of them. Oh, auto or motor...very strict about maintenance schedule and quality of products used.

The one thing I tell people about Octane... it doesn't give you improved performance, it helps protect your motor and keeps it running in its original manufactored condition, or as close to it as possible. If you want performance then you have to add and subtract engine components and go through tuning via Dynomometer.
Honestly, all the bikes being manufactured today are suppose to meet a strict emissions guideline and motorcycles are becoming more and more tamper proof with catilytic converters, sensor technology and these new valves (for all you Harley Riders) that create way more torque than horsepower because they don't open during the exhaust portion of the 4 stroke compression process.
The EPA demanded it of the car companies and it was only a matter of time before they got to us!

I know there are still some fuel vendors in TX with unpolluted fuel.  I've seen them, just can't remember off the top of my head  who it is.  Must be gettin old. 

I've always used 91-92 in my old shovelhead, and was wondering what I was supposed to use in my new Ultra Classic.

Thanks!

Hypno, You should be running 91 or 92 octane in the new bike as well. I believe the HD owners manual calls for 91.

Like most folks so far I run 91 (93 as 91 is not availabe but at a few stations around here Mass.) This is what Harley calls out for in there twin cam engines. The one thing to watch for is the ethanol mix in the fuel. Presently a twin cam harley can take 10% mix of ethanol and 90% gas. Some are starting to play with 15% ethanol which i'm not sure how well it will take to.

Thanks BailOut - That is what I am getting from the discussion. I tried the gas that is one step down from premium and she started rattling. So you all are definitely right.

Alright, I'll throw in my 2 cents, and keep it short on tech stuff, since there's been plenty of good input.... On the bike, I use mid-grade, and have noticed a decent boost in milage from when I use regular. However, in my truck and van, I do something a little different... I do put 87 octane in, but for every 5 gallons, I add 1 napthalene moth ball. This does several things, including but not limited to (lol) boosting octane into the 90's, cleaning carbon deposits in the cylinders, cleaning carb jets and fuel lines, removing water (from condensation) from the system, and acting as an fuel anti-freeze. I have been doing this since I started driving, learned it from my Dad, who I believe learned it from an old stock car racer. I've NEVER had one of my old carb-run vehicles fail to start in cold weather, I get excellent longevity from my spark plugs, and over-all, my old trucks run very well and have above average fuel economy.

I have to say that this WILL NOT WORK if your car, truck, or bike is equiped with a catalytic converter. The harmful carbon deposits that the solution takes care of comes out in a black stringy substance that is not a problem for your exhaust system, but will foul up a cat if you make a practice of it, and that's an expensive mistake. (of course, they're worthless, and if your area doesn't have emisions testing, I'd take the thing out and replace it with a small peice of flex pipe)!

To be back on topic, if you have a newer vehicle, the best rule is to follow the owner's guidelines, I know for a fact that not all modern engines can tolerate good gas; for example, I know someone who managed to blow up on the early PT Cruiser by putting 93 octane in it. The aluminum cyclinders softened too much from the heat, and it was cooked. (at least that's what the dealership mechanic told him when he tried to turn it in for warranty work!) Follow the instructions, and you should be in good shape.

it's not a dump question either, yup where we don't need such gas equipment in more amount. If do have needful check out all its requirement regarding to put in there proper amount. I would like to share something that sometime we or you are looking for the best kind of motorcycle apparel today?  If you do, then you don’t need to settle for anything else, because what you need is the one that is just right and fit to your needs right now.

There are so many different kinds of motorcycle apparel that you can see in the market today, but of course you need to look for the one that you think is best for you so that you can assure that the one that you are buying for is with high quality to trust.  Quality is very important so that you can ensure that it will last for a longer period of time, since you are going to use it in your everyday lives.  This is a very practical way that consumer is thinking about, a long term use.  So, why buy a cheap price of apparel right now when you can buy higher cost but have a quality to rely on, just like HJC Helmets.  This is a good example of quality apparel that can trust about.  With this kind, you can assure that your everyday travel can be safe and protected because you have a high quality kind of helmets to use.  Helmets are a good protection while driving for a motorcycle.  Therefore, don’t just settle for anything else, most especially if we are talking about one’s safety.  This is not only apparel but a safety gear as well that matters life. 

What is important right now is that, you are smarter and wise in choosing the right one and the best thing that you deserve.  Even though there are so many brands and offerings in the market, still you are looking for the best quality that you can rely on.  So that you can feel all the confidence while you are driving on your way.

Am in Muskogee, OK just now.  Saw Phillips 66 station advertising no alcohol in premium gas.  I would think that any phillips 66 station would have the same fuel as any other.  Am I mistaken here?

here is my 3cents, when I had my 86 883 I use mobil 93 all the time ran great. then bought a 87 fxlr custom lowrider and ran the same mobil 93 to this day I still have both bikes, one with 69k on sporty, 42k on fxlr.
Just a year ago I bought the fatboy lo and from day one sunoco 92, along with amsoil 20-50. so running 91-93 grade of gas will not hurt your bike harley's, other bikes not sure some of them call for lower octane.

All I'll add at this point is that it does take compression to ignite octane and lower compression bikes will not burn high octane fuels and the end result is like raw fuel blowing right out you're exhaust. Heavier oils do increase compression and if the oil is too heavy you sacrafice lubrication. So if your going one weight higher in oil you may notice an increase in power if you have higher octane than needed.

Also, in cold climates you're better with the lowest octane the bike will handle with adequate performance in that the lower the octane the higher the burning temp (btu).

If the OEM says that the best octane for your bike is this or that then use it. You can go one octane higher if you're riding two up. The issue isn't with octane, the issue is with additives the oil companies put in the gas. In the northeast stick with SUNOCO no matter what the grade, you shouldn't go higher than what you actually need, and be assured the right additives are in it for the geographic area you're in. Citgo is another story, they allow the dealers to order the additives they want in the gas and most dealers won't spend for better fuel. You're fuel economy takes a dive and they make more $$$ from their discount gas sales then you could imagine with all the additional fillups you'll need.

Now then, immisions plays a major role in what OEM's reccomemd for octane. They reccommend 91 for my bike and I've used 92 & 93 octane gas and really found very little difference, if any, in fuel economy. Since I have a high mileage bike with a minimal amount of ring and barrel wear, never the less enough to drop compression, I use 87 and have no major problems. Sure, as a bike loses compression you do lose power, however, mine just keeps on pulling. I use my unique blend of oil and it really works quite well keeping wear at the trivial level. Soon, I'll be over 100K and then I'll really take a look at the performance issue and give everyone some feedback.

All in all, don't by cheap gas. Stick with the major brands and you'll do alright.

Gas!!!! The best gas for your motorcycle is any gas without the ethanol! Most gasoline on the market today has 89 octane fuel advertised as marine fuel that has NO ethanol. Ethanol, if not used within 30 days, starts to break down. Water seperates from the alcohol (ethanol) and starts to ruin your entire fuel system. Put a fuel stabilizer in your fuel if your bike will sit for mare than 30 days. I can tell you of many problems associated with ethanol for those who are interested.

Not sure if anyone has mentioned this part... If I see a tanker in the station dumping fuel I pass and find another station. When I fill up I always try for 93 octane. Perfomance, MPG are a win win in my book.

Best fuel to use and I use it whenever I can find it (not easy in IL) is Ethanol free gas. Will give you better milage, more power, less knocking - all around better for the engine. I use premium on all my engines. Ethanol will destroy rubber parts on older bikes unless they are exchanged for ethanol resistant ones, Ethanol will gunk up your carbs if stored without additive for extended period of time. Ethanol is a degreaser and over time will dilute your engine oil so it is important to keep up the maintenance schedule on oil changes. Ethanol is supported by politicians and taxpayer money but has not done anything for the environment - they add 10% and your milage goes down 10% - explain the benefit to me?

Every state seems to have their own mix for summer and winter and regulations to go with it, which is part why gas prices are all over the place (manipulated by big oil of course in their favor) - unless we go full ethanol like Brazil and modify all engines to run on it it has not done anyone but politicians and big oil any favors. My 2 cents.

Long answer for premium all the time

My 04 HD Sportster Owner's Manual says use 87 octane for all 883 models and 91 octane for all 1200 models. I wonder if the Big Twin engines call for a higher octane? When traveling I use the highest octane I can get usually 91-92 but it averages out as you get out to the midwest and there are a lot of 87 only gas stations. I see a difference in a tank of 87 than I do with the 91. I do travel with some octane booster and use it when I have multiple fill ups with 87.

The octane rating of gasoline is the ability of the gas to withstand compression before detonation. It is very important to use high octane gas in high compression engines because if you don't, the fuel will ignite by the force of compression rather than the spark. This will cause knocking and can severely damage the engine.

On the other hand, using high octane gas in a low compression engine is a waste of money. High octane gas is not better gas. It is simply formulated differently.

The best way to determine what octane rating to use in any vehicle is to follow the manufacturer's recommendation.

With my 400 I use the highest I can find premium and ethanol free.  It won't run very well on anything less.  My 1300 I use Mid Grade it had some engine work done and no longer likes premium or regular grade fuels. Also I try to use ethanol free in it as well if I can it likes it better.

Here in Portugal we have 95 octane ($6.61/gal) and 98 octane ($7.25/gal). Costs about $0.50/gal less in Spain, $0.50 more in France and $1.50-$2.00 more in Italy. (Paid $10.53/gal for 100 octane in Italy last year)

In the heat of summer sometimes 95 will ping a little when accelerating on the highway. 98 always runs smooth.