Gas?

[XS1100_OEM4ME]

I have read on here that many use reg. gas in their XS1100's for best preformance? Where I live, that would be 86-87 octane? the spec's under my sidecover DO say reg. gas BUT is also say min. 91 octane (as most reg. leaded gas in 1979 would have been 91+ oct and top prem. gas like Sunoco 260 was 104+ octane. With todays fuel I would need to use prem. to get a 91+ octane fuel. Why do so many recomend sub 91 octane. Any reason other then $$$ to do that with a 1979 9.2 compression motor?

[DiverRay]

The gas was rated with a different formula in the late '70's. Use regular, but stay FAR AWAY from the ethanol laden regular. If you try premium, you WILL carbon up the engine, and raise the compression ratio, and have a lot of fun cleaning things on down the road. You CAN use the mid-grade if you have problems with regular, but I still just burn GOOD regular gas in my 1980 MNS with no problems.

[bikerphil]

I use the 89 mid grade. The 87 causes ping on my engines with WOT in top gear. I also have my timing up a degree or two to gain a little low end pep, YMMV.

[XS1100_OEM4ME]

ethanol

I live in SW Florida where ALL gas is 10%+ ethanol They even mix the stuff in the prem. gas. Don't know why, could have something to do with being at sea level. I know the octane rating system changed, it had too as lead was used to increase octane back in the good old days But I thought the current rating system was still to provide octane #'s for compresion ratio'sMy cars all say prem only and they have 9to 10+ compresion ratio's. The cars that I know of that can run safly on reg. have 8 and below compresion ratio's

[crazy steve]

Octane requirement has to do with compression, but timing enters into it too. So a newer vehicle with a 'lower' ratio still may need a higher octane to run right.

The XS11 was originally designed to run on 'regular' grade fuel, which in those days usually ran around 92-93 RON (Research Octane Number) in a major brand. The current rating is an average of RON and MON (Motor Octane Number, which is always lower than the RON number), so the 'new' number will be around 87-88 as listed on the pump. If it doesn't knock/rattle on regular, that's all you need.

If the bike is out of tune, carboned up, or has a bit more timing dialed in, you may need the mid-range. The SG I recently finished ran great on regular, no problem....

[XS1100_OEM4ME]

gas

Thanks Steve, I guess I will move to mid grade and see how it works, any thoughts on the high content of ethanol I am stuck with? What are the down side of having to use it?

[crazy steve]

...any thoughts on the high content of ethanol I am stuck with? What are the down side of having to use it?

Ethanol attacks some of the rubber and metal parts in the fuel system. The effects on the metal are minimal, it's more of a problem with the rubber parts, although if the carbs have been rebuilt recently with current kits the kits should have had the newer type 'good' rubber. It seems to be more of a problem on cars/trucks where you have 'wet' diaphrams in the fuel pumps and carbs. The diaphrams on our CV carbs aren't exposed to the fuel, so it's not a worry there. Usually if ethanol is added to any fuel in an area, you'll find it in all grades, so stepping up to a higher grade won't do anything to help the ethanol 'problem'.

The other thing to remember is octane rating is actually a measurement of 'burn rate', and as octane goes up, the fuel burns slower. Higher octane fuel actually contains less 'energy' per pound compared to lower octane fuel, so running a higher-than-needed octane can reduce fuel economy and power slightly (because the slower-burning fuel won't completely burn during the power stroke), as well as contributing to faster carbon build-up.