Fuel Octane

Fergie · Posted: August 5, 2008, 10:44 am Post subject: Fuel Octane

I run 87-octane in my bike, and haven't really had any complaints other than it vibrates pretty hard from 3500 to 4300 rpm. My dad just took his first group bike trip (300+ miles) with some buddies from work on his '78 kz650, and they told him to try 92-octane and see how he likes it. He told me that it smoothed out the end, made it easier to start, and gave him 5 points better MPG.

As far as I know, my engine is bone stock, and hasn't been rebuilt in 26 years, but I don't know how many times it's changed hands before I bought it. Usually as an engine ages you want to use higher octane fuel to protect against knock as the carbon build up in the combustion chamber will raise the compression ratio. I haven't heard any knocking going on, but I only have a gallon left in my tank, so I might just fill up with 92-octane next time to see if it positively effects my engine.

What does every one else run in their bikes?

BigGeorge · Full Member Joined: Apr 13, 2008 Posts: 267

I run the high test. Lots of hills where I live and the bike will ping when under a load on the 87 octane................BG

killer · Posted: August 5, 2008, 7:51 pm Post subject: Re: Fuel Octane

I run 92 usually... keeps the pinging away.
I sneak it a little 100LL from the old man's Cessna when I go to the airport.

rsylvstr · Full Member Joined: Aug 09, 2008 Posts: 65

do you have to run with a lead substitute?
the manual doesn't say anything, but a sticker in the airbox says, "91 octane leaded fuel"

dps-rider · Full Member Joined: Aug 25, 2007 Posts: 100

87 octane is too low for these and using it is asking for trouble. Use high test.

rsylvstr · Full Member Joined: Aug 09, 2008 Posts: 65

so should 93 octane WITHOUT lead substitute be OK????

nj1639 · Posted: August 9, 2008, 9:53 pm Post subject: Re: Fuel Octane

93 unleaded is all that goes into mine.

raftercliff · Posted: August 10, 2008, 12:05 am Post subject: Re: Fuel Octane

I read an forum discussion somewhere that discussed this. If I understood correctly, the important part is the octane because the higher octane retards combustion. The lead that was added to gas in years past had this same effect so that is why leaded fuel was recommended.

I also read a letter from Yamaha stating that unleaded fuel was perfectly acceptable in these bikes. So, use the higher octane and all will be well with your bike.

xsjohn · Posted: August 10, 2008, 12:08 am Post subject: Re: Fuel Octane

Even 93 octane is junk........but what can we do......buy aviation gas ......not me.............

xsjohn

raftercliff · Posted: August 10, 2008, 12:11 am Post subject: Re: Fuel Octane

I found one of the references I mentioned above. Here is the link.

www.excess650.co.uk/un...%20(1).htm

xsjohn · Posted: August 10, 2008, 12:18 am Post subject: Re: Fuel Octane

Pinking sounds......would that mean the bike is gay...............xsjohn

What Happened to 650rider.com?

Yamaha xs650