Proper octane for GZ

[bonehead]

Hey guys and gals, I just surfed thru the service manual and on page 9 it states "Use unleaded gasoline that is graded 91 octane or higher. Now which is right, the owners manual or the service manual? (This aught to start a frenzy)

[Easy Rider]

Originally Posted by bonehead

Hey guys and gals, I just surfed thru the service manual and on page 9 it states "Use unleaded gasoline that is graded 91 octane or higher. Now which is right, the owners manual or the service manual? (This aught to start a frenzy)

No, no frenzy at all. It takes regular grade, unleaded gas. In the US that is 87 or 89, depending on what part of the country you are in and what company; some don't carry 87.

That particular service manual is either a mis-print OR it is an English European version......where the octane is measured differently which results in higher numbers......for the SAME regular unleaded gas.

[/frenzy] :cool:

[Water Warrior 2]

Use 87 octane. There is no reason to spend money on a higher octane gas. Keep in mind the GZ is a major form of transportation in many parts of the world where lower octane is the "only fuel" available.
The comment by Easy is probably correct.

[alanmcorcoran]

I have another bike that really *does* require high octane. It pings a bit if you put in the low octane stuff. I followed Easy's advice on the GZ and never had any pinging. The ethanol issue is probably a little more "volatile" than the octane one. We don't have much of it out here so I haven't had to deal with it.

[dhgeyer]

Octane ratings can be confusing, because there are different methods of measuring them, which give different numbers for the same fuel. "Research Octane" gives a higher octane rating for the same fuel than "Motor Octane". "Pump Octane" is a combination of the two methods, and is what is posted at the pumps. I've had several manuals that call for 91 Research Octane rating specifically, and that tends to mislead people into thinking they need high test fuel. Fuel with a Research Octane rating of 91 will have a much lower Pump Octane rating, and is probably what we know as regular. Most manuals spell this out in one way or another, although not usually clearly.

The GZ250 owners' manual posted on this website in PDF form simply says to use regular fuel with an octane rating of 87. Absent any qualification of which octane rating they refer to, you may assume they mean the "Pump" octane rating.

Engines that require high octane fuel usually have higher compression ratios than the GZ, larger displacements per cylinder than 250 cc's, or in some cases the shape of the combustion chamber can make an engine more susceptible to knocking. Nothing about the GZ250 engine design makes it a candidate for high octane fuel. That's one of the very nice features about it from my point of view.

[GZ250]

use JET FUEL

[burkbuilds]

Originally Posted by GZ250

use JET FUEL

Do NOT use jet fuel, which is basically kerosene, the GZ will NOT run on that. I'm sure that was probably said completely in a joking way, but just to make sure nobody misunderstands, enough said.

As long as you don't hear any pre-detonation (pinging)(knocking) you are using gas with a high enough octane rating and 87 has never "knocked" on me in the GZ. A lot of people think they will get more power out of high octane gas, but it actually has LESS energy in it than the lower octane. Think about it, what did they used to put in gas to raise the octane and prevent it from detonating before the spark plug fired? LEAD, lead is not combustible! Lead simply made the gasoline less volatile. Back in the early automobile days(early 1900's) engines were extremely low compression because until modern refineries came along gas had an octane rating seldom higher than about 50, and it would detonate from compression rates way lower than the GZ. Now if you have a high compression engine, you need fuel with a high octane rating or it will explode from the compression before it gets up to top dead center or a little past it and that is NOT good. As several people have pointed out, the GZ is NOT a high compression engine and you do not need high octane fuel.

[jonathan180iq]

It's probably because I'm poor, but I've never had a vehicle that REQUIRED anything more than regular unleaded. Good 'ole 87 octane fuel for me. It's also what's RECOMMENDED in the service manual. That means that you can use whatever crap you want, provided that it's petroleum based fuel and meets at LEAST 87 octane qualfiications.

On a side note, I have years worth of fuel economy records for all of the vehicles that I have owned and I have never noticed a difference when it comes to comparing one tank of regular against one tank of supreme (93 octane) fuel. I know this goes against the science, but there was not a measureable difference. The only time I've ever recorded increased fuel economy was when I found a gas station that sold fuel with NO alchohol in it. The difference between regular and supreme was never high enough or low enough to fall outside the realm of NORMAL.

[alanmcorcoran]

jon,

I once owned a Datsun 310 - basically an economy vehicle. It knocked like crazy if we didn't feed it the good stuff. Of course, the good stuff only cost about a nickel more (like 69 cents) back then and wasn't that big of a deal. The Yamaha will also knock (or ping) if you forget and put in the lower octane. Not an economy vehicle, but it does mean that it's not just a "recommendation." The pinging and the knocking usually only happen when you are putting a strain on - like climbing a hill.

I filled up at Ragged Point when I went to Monterey a few weeks a go. 91 Octane was $4.70. I was glad I only needed about 3.5 gals.

[music man]

Originally Posted by alanmcorcoran

jon,

I filled up at Ragged Point when I went to Monterey a few weeks a go. 91 Octane was $4.70. I was glad I only needed about 3.5 gals.

Gas is still 4-something a gallon out there where you live AlanC, HOLY CRAP!!!!! its been hovering at about 2.20-2.30 a gallon here, of course that is for 87 octane but still.