As others said, premium is not needed unless you run a custom cdi with way advanced timing and worry about knocking (predetonation). This is a world bike made to run on 3rd world fuel. That said, I'm not a fan of U.S. corn fuel ethanol added gas, but still works fine and though to avoid in most states.

 

I'm not trying to be snarky here, but what makes you think that?

 

The shop I bought my bike from said not to use Premium because it is not a high compression engine. In Aus we have 91, 95 and 98. He said to use 95, and if that is not available then use 91.

 

Hemming's Motor News - click - lays it out. No benefit to higher octane. Nothing about running cooler or cleaner. And Hemmings is all about vintage and higher performance cars.

Lemmy's article from Revzilla : The important takeaway here is that octane itself does not cause the power, it merely allows an engine to make power if it’s built to do so. Using high-octane fuel in a standard-compression engine won’t give you one more lick of power. I contacted a technical specialist for a manufacturer who’s a good friend, but needs to remain anonymous. His reply in regards to high-octane go-juice in a low-comp motor in search of power? “Often it has quite the opposite effect. It takes more energy to ignite the fuel, resulting in power loss.“ click

SuperChevy: Octane

A fuel’s octane number is its ability to resist detonation. And it’s important to note that octane isn’t power—the benefit to raising a fuel’s octane quality is only valid if the engine it goes into is detonating. The higher a fuel’s octane number, the more resistant it is to detonation. An engine only needs enough octane to prevent detonation; if it’s tuned for 91-octane pump gas and has a slight ping on a hot day, filling up with 118-octane race fuel won’t add crazy horsepower. click

Unless you're screwing with advancing the timing, higher octane than is needed is a waste of money. Use your ears. On my KLX650 it was a bit sensitive, in the summer on really hot days it would ping on 87, but not so in the cooler fall/winter/spring. I'd run 91 just because, but woutd have to step up to 93 in the hot summer. Not had any pinging with the 250 so it gets 87 and seems to be really happy with it. I had the dealer recommend using premium in my XSR700, but seems Yamaha says 87. With the engine management it has, that the 250 doesn't, I will probably go with 87 or 89.

Cleaner burning has to do with using the top tier gas. Top level formulations that have nothing to do with octane and everything to do with the additive packages, the blend. Kind of like how you find certain brand fuel doesn't seem to run as well, obviously avoid that brand.

 

I had issues with knock riding during the summer on 87 octane gas in my KLR650 (I live in Phoenix) so I switched to mid grade (89) during the hotter months. No more knock. My KLX250 gets such great mileage, I run 89 octane year round in my KLX250.

 

Most of these guys that are having knock, probably have never rejeted the carb to proper fueling from stock super lean to the max!

 

Excellent point. The other point is to know when to go to higher octane rather than automatically doing so. The money saved running a lower octane would quickly pay for the jetting. One article pointed that out about using race gas. Their comment was about doing higher performance parts that would still allow pump gas... like a 351 kit or a pumper carb.

 

The KLR650 is more prone to detonation than the KLX250. A good bit of the reason is the larger combustion chamber and that challenges the flame front vs. the smaller combustion cylinder of the 250. Now, that's not a consistent recipe across the board as it applies to 250's or 650's, but it is in the case of these two. That said, most properly jetted KLR650's will run regular U.S. fuel in most conditions but when they get lugged down in the rpm and you crack the throttle without down shifting, it's not unusual to hear a bit of pinging and that can occur even with premium. I've had four of the KLR600/650's, and would/could get a little pinging when I was lazy with the throttle and clutch.

On the octane level and compression ratio of the engine, here's an interesting issue. I have several friends in my area who race highly modded ZX1400 drag bikes. Some turbo'd, some NO2, and some both. Most of them are setup to run regular octane gas. I thought that sounded crazy, but it was explained in some form about the short duration, high rpm, and other issues that allowed the regular octane gas to produce more BTU's without cooking the pistons. Not my area of expertise, and I think I only vaguely comprehend it. So many of us are indoctrinated to run higher octane fuel for real and/or perceived reasons in our motorcycles.

 

I was indoctrinated until I learned the reason for the higher octane. Then I quit automatically doing 93. Now it's 87.

 

On the various m/c forums I've been on over the last 23 years (KLR650, VFR750, FZ1, XT225) when the subject of octane level has come up, the consensus has always been: The lower the octane you can use without pinging under load, the more power and the better the mileage will be. I know nothing, but the m/c's I referred to, as well as my current KLX250S and GL500i, have always done just fine (no pinging) using 86-87 octane.