I view this topic like the various opinions on oil/etc. I run premium in my 99 because it runs smoother and gets a little better milage. Only mods I have are Speedstar ignition, Roadhouse Dooleys, and Kury Twin Velocity with the K&N filter. And the necessary rejet.

Regular grade and

Engines need higher octane gas because low octane fuel will pre-ignite under the higher pressure and temperatures of high compression engines. (That's why diesel engines, which have very high compression, do not need spark plugs. The fuel ignites as soon as the injectors shoot it in there.)


If you don't fit into that category (hig compression) and still decide to spend the extra money - well, the oil companies will love you, but you aren't doing your engine any good (or any harm, as far as I know).

I am running the stage 1 on the stock exhaust and mine runs better, idles better and gets better mileage on the 89. It might cost 10 cents more a gallon, but that is less than a 3% price increase for a 5+ percent increase in mileage. It just pings all day on the 87. I tried 92 and 93 with no appreciable difference. That was just a waste of money.

Had to take a test ride today to see how the jetting was so I said screw work around 10:00 and went for a 150 or so mile test ride . It seams to be right on from city trafic to open road 80 mph cruising , Wife says im still smiling . What a blast ! Used reg. fuel and it seamed fine . Just one or two caughs on take off but nothing consistant . Got about 160 miles on when I got back and the gauge said around 1/8 th left so I dont think its running to ritch or to lean . Pretty good improvement with pipes , intake & jetting . Any coments on AIS removal ? Pros or cons ?

I started using 89 octane after the Yamaha mechanic told me I should, because it is a high compression engine. Seems like it cured my puking problem too, or else it was that MMO that I added two tanks ago.
Go figure!

There is more butane on the higher grades (lowers the flame-speed and therefore raises the "octane" rating. "Octane" is not an actual substance, it is only a "rating" of resistance to pre-ignition.
Higher "octane" rated fuel burns SLOWER, and is harder to ignite. This is why it reduces "knocking"
The hot carbon deposits have a harder time igniting it, the compression heat has aharder time igniting it. And when the spark plug does ignite it, it burns SLOWER, so it doesen't smack the piston so hard at the wrong time... reducing pinging or knocking o pre-ignition.
Most RoadStars do not have high enough compression ratios to need premium fuel. But my own experience has shown that on REALLY HOT days, some engines will run a little better on premium, due to the extreme heat that might cause them to "knock" around town in heavy traffic.
Premuium fuel contains more "butane" which atomizes a bit better, and burns a bit slower.
If you use premuim fuel and you don't need it, you are wasting your money.
If you find it makes your engine run better in hot weather with less knocking, you are not going to hurt the engine by using it. Knocking, or pre-ignition is pretty hard on the rings and pistons if it is severe enough.
I think most "carbon problems" come from running too rich, running too cold,
and "LUGGING" anngine under heavy load. Lugging is probably worst next to running too rich.
(In lugging, the flame gets snuffed before it gets everything burned.)
I can usually use regular most of the time, but on really hot days I will stick to mid-grade or higher.
That's just what I find works good for me. But I'm very careful with my bike, and how I run it.
Gasolines are not all the same as brands differ. And you have to know the difference between "pump octane" and "research octane" ratings. If gasoline is more than 30 days old, it's "octane" rating declines rapidly, as the butane escapes and the gasoline deteriorates. In some cases I can see some people having to use higher grades to compensate for many factors that are beyond.
Ever since they took the lead out of gas, we've had poor "octane" ratings and gas that spoils rapidly.
That's why avaitaion-gas still has lead in it. Aircraft gasloine engine technology hasn't changed much in the last 50 years to allow unleaded, poorly graded fuels to be used. There's too many risk factors involved when you change something that works, and is tried, tue, and proven to be reliable for safety.

Just to clarify.....Stock Roadies are Low compression motors. That means they require no special fuel. Adding pipes and air boxes and Manifold and ignitions does not make your R* require high test. They still need just 87. If your motor has been built (meaning someones replaced pistons , etc...with performance parts , HC stuff) , then by all means , give the girl what she needs. Otherwise , you're just fattening up someone else's 401K. Word to the wise. BB

Big Bear wrote:
Just to clarify.....Stock Roadies are Low compression motors. That means they require no special fuel. Adding pipes and air boxes and Manifold and ignitions does not make your R* require high test. They still need just 87. If your motor has been built (meaning someones replaced pistons , etc...with performance parts , HC stuff) , then by all means , give the girl what she needs. Otherwise , you're just fattening up someone else's 401K. Word to the wise. BB

Yep.