Is it just my imagination, or.........

[pinhead]

I am getting ready to do major service on my BMW K100.  replace temperature sensor, replace tires, (and brake pads if needed), change spark plugs, etc.  So I decided to take a spin up to the Sierras as far as the snow line.  Now I had what I thought, noticed a weakness in the power out put on this bike when I rode on the freeway a couple of weeks back.  It was not missing or backfiring, just didnt seem to have the power to get up and go.  So I am thinking I might have something else to fix also while doing the rest of the stuff.  Anyway, on this last trip I decide to use the super grade of fuel, bypassing the cheaper regular fuel.  I noticed, unless I have a distorted imagination, a real power improvement.  Now I know the high test fuel is used primarily to prevent pre ignition or pinging, and I had nothing noticeable like that going on with the many times I filled it with regular.  So to get to the point, what grade fuel do you use and is there any difference in performance on a K bike?  Now I forgot to mention I live in CA where the fuel blend could be more squirrelly and a mid west fuel source. 

[The Mighty Gryphon]

There are essentially two grades of fuel that I use.  87 octane E10 regular and 91 octane corn-free.

At one time I used only the corn free, but now I just run that at the end of the season so the bike is stored with it.  I really don't see any real performance difference between the two grades, but then, I ride like an old fart, shifting at 3500-4000rpm.  I do a fair bit of highway riding at 65-75mph, and performance at those speeds is pretty much the same whatever I use.

If there is a difference, the expensive stuff might get an extra 1 mpg over the cheap stuff. 

[sooprvylyn]

I always use premium in my K.  I know it will run on standard, but heck, its only a couple bucks more since Im only ever putting in like 2-3 gallons at a time, and it doesnt seem to give me any issues so if it aint broke...  I dont know if there is any power difference since I never use standard fuel.

As for your power "weakness"...was there any chance you were at high elevation when you noticed the drop?  Have you checked your air filter to make sure its clean?  Is your fuel filter good, might it have had a little blockage in it?  Your brakes arent sticking at all(youd probably notice them smoking if they were)?  Anything else and might be TPS or hall effect sensor related...or something else going on w your ignition system.

[sooprvylyn]

lastly possibilty on the power thing....probably a long shot, but hows your clutch?  If its really worn or glazed this could potentially cause some issues.  Usually that would be felt in torque tho since the slipping would be more apparent as you roll on throttle more quickly rather than gradually.  You can easily test this. If your bike has its get up and go from a stop your clutch should be fine, but if it doesnt seem to respond quickly to throttle input you might be ready for a clutch friction plate change.

[frankenduck]

Never hurts to run some Techron concentrate added to the gas every once in a while.

[Chaos]

it's possible the hi test had no ethanol in it, that could get you a little extra oomph if you previously had a blend.

[Laitch]

It's the placebo effect. Enjoy it.