gas preferences

My "82' xj650 seca seems to accelerate better with premium gas. Watch out for regular with 85 octane.
All my bikes start to bog on it after about 200 miles. I have to add a shot glass of sea foam to a full tank
.to get power back. also the mileage gets worse the more ethanol in the mix as is witnessed in the upper midwest "corn belt"

 

I suspect that you have some underlying issue.
I use the lowest octane at the pump, and E10 when available. No difference from using higher octane fuel.

 

my bike sounds different when i run non ethanol high test
gas mileage is the same with 85, 87 or hightest.

i use the non ethanol high test at the end of the season with the expectation of winter storage
to get the ethanol blends out of the system for storage

 

There are only a few places around me that sell non ethanol gas, and they require membership. I run premium e10 all the time and have no issues. When I got the bike I was told that's what he ran in it. I heard that with air cooled engines that premium is better because they run hotter and there are additives/detergents/whatever that help prevent preignition and all that jazz. I don't know if that is true or not. I have done mid grade as well, and I feel that the bike pulls a little stronger with premium, but that could very well be a placebo thing.

 

higher octane is for high compression motors
additives/detergents are in most brand name fuels and in my area it is the same truck delivering to the no name stations and brand name stations

 

On long distance rides in the wide open west, I noticed going to reserve faster 0n 85 octane vs premium with
no ethanol. On my valkyrie it's sputtering at 95 miles from a fill with 85 but I get close to 120 with premium.
the worst gas is the moonshine they serve up in South Dakota. I hope I haven't offended any corn farmers.
yes, Valkyries get shitty mileage.

 

mixing apples and oranges comparing honda to yamaha
i keep a gas log 50 mpg with any type gas

 

Etahnol blends do return lower MPG than non-blends (usually around a 3% loss for E-10). Ethanol is less energy-dense than gasoline.
It does have the advanatage of increasing octane for very little cost though (and without the groundwater pollution issues of MTBE, or the brain damage caused by Tetraethyl-Lead). A high-compresson engine, boosted, and tuned to run on E-85 is a beastly powerhouse that will outperform a similarly built gasoline engine.

Tradeoffs; everything has some.

 

as XJ550H and K-Moe stated, your XJ should run fine on regular. If you don't hear pinging with regular you're wasting money buying premium gas.
Here in Ontario our lowest octane is 87, nice to know the 85 works fine.
I had this discussion with my brother who moved to Norway and took his motorcycle with him. The European's use a different octane rating system so our 87 regular is equivalent to something mid-90's over there. He was convinced his bike ran so much better on the Euro fuel.

 

Standard octane rating in the UK is 95-ron, up to around 98 for 'supreme/x-power' fuel.