Good one, Will

I've run lower octane at times. Always seems fine, but got a little knocking with the 85.5.

Yeah, I know the higher octane is for higher compression. The higher compression can produce more power, but not the gas itself.

I was wondering if going up in octane could have thrown the ECU off so much that I got that rough idle and stalling.

Bad gas makes more sense, though. The place is call Kum-n-Go, after all.

 

Eggzactly!

 

Yup, the higher the octane, the LESS combustible the gas is. You can always run higher octane (within reason) because the spark plug will ignite the fuel anyways. Lower octane in a higher compression engine will ignite the gas early because it's literally compressed to a point where the molecules heat up and ignite.

the higher power comes from the higher compression. The same amount air and gas compressed into a smaller area and then ignited will yield higher energy.

 

Gotta disagree with your first paragraph. Whether or not your bike seems to run fine is totally dependent on the engine management system adjusting for detonation. As soon as the knock sensors detect detonation, your spark will be retarded to prevent detonation. If you are not running at full advance, you are losing power and gas mileage. There is only so much it can do, however, and if it's already retarded your spark due to the low octane, and you get into a lugging or high heat situation, you may have used up your engine's ability to compensate, and detonation will occur.

Run what your manual tells you, which is a minimum of 91 octane.

 

I always run 91 octane. Not sure if it matters or not but the price difference for such a small amount, I just figure "what the heck, why not?". I used to try and fill up at a "premium" station but in the last several years I just fill up anywhere.

 

Sorry but, it recommends 91 octane. My '09 Road Glide runs quit nicely on 87 octane.

 

I run 89 in both bikes(01 is carbed and 06 FI) with no problems so I dont see a need to change.....Even new cars/pickups recomend 87 due to the ECM's,heck even new boat motors recomend 87 oct.....

 

maybe a dumb question but is your bike carburated and are you still at low alltitude?

all gas is the same, only the additive is different.

 

What % of the gas was Ethenol? That stuff attracts water and if its an old batch that was in their ground tanks for awhile, it probably sucked some up. With all the rain (and snow!) that you have had lately, that could be the problem.

 

With EFI it will run just fine on lower octane because the knock sensing will retard timing and run the mixture richer to compensate and prevent damage if it starts knocking. Both actions reduce power.

On a hot day or with a heavy load EFI will pull back and you won't be getting rated power from your engine. It will run OK and it will not suffer damage, but do realise that the engine won't be making full power.