Fuel: 91 or 96?

[T-Thunder13]

ive been putting 91 octane in my xr since i bought it and have never had any running problems but i was just reading in stroke mag that the higher octane level the better for you bike. so im gonna make the swich. my question is, is it nessisary, and will it afect the jetting of the bike or cause any problems at all?
cheers for any advice!

[xwhatsit]

In road bikes at least I've never heard of it affecting the jetting. It shouldn't, the difference between the fuels is a matter of different additives, which is a tiny amount (by volume) with respect to the overall amount of fuel. So you won't be changing the fuel to air ratio appreciably.

A higher octane level simply reduces the chances of detonation. Does detonation occur on your bike? Does it overheat? Have you upped the compression ratio a lot, or made significant other internal engine modifications? If not then there's not a whole lot of reason to. XR250Rs are not exactly so worked as, say, a YZF250 or somesuch, are they? I mean, the engine is relatively mild and you'd go a very long time before rebuilding it?

[Big Dog]

The supposed benefit of higher octane is that it burns colder.
This means that when your going hard you will not hear your enging "pinking".
This usually only affects high compression engines when at high rpms.
Most bikes will experience no benefit, unless they take advantage of the fact that they can burn more fuel per RPM without engine heating.
On a long ride on a sunny day I pack 98 as the temp gauge stays a good 10% lower.
Rest of the time I run 91, unless it starts running rough. This last part is becuase I have a BP fuel card and they put no detergents in their 91, meaning if this is used exclusively without using injector cleaner your injectors get clogged. The occasional tank of 98 costs less than injectors or injector cleaner, should make little or not difference to carbs.

[Big Dog]

Oh and 2 stokes have been known to experience some "power gain" on 98 but this is usually accompanied by a parralell fuel consumption increase.

[Wellyman]

I ran a mix of 98 and Race Gas (Av Gas) in my Gas Gas. and it does have a bit of a power increase, but not major.WM

[Grub]

i was just reading in stroke mag that ...

Isn't that a gay wanking mag?

I run either 95 or 98 in the CBR but I used to run it on 91. 70% of my gas is 98 and I can confirm that I get 1.5km/ltr better fuel economy with the 98. The added benefits beng cleaner cooler running. Once you tot it up, because of the better economy, it costs the same to run.

[dammad1]

Hey tom, I only run 98 in my bikes, its probably more piece of mind than anything but because the higher octane fuel has a more stable burn it decreses your chances of pre ignition or detonation which is something you definitely want to avoid.

Your XR has had a few mods, so it definitely won't hurt it.

[_Shrek_]

ive been putting 91 octane in my xr since i bought it and have never had any running problems but i was just reading in stroke mag that the higher octane level the better for you bike. so im gonna make the swich. my question is, is it nessisary, and will it afect the jetting of the bike or cause any problems at all?
cheers for any advice!

if i run 91 the bm runs rough as guts 95 runs well but get better ks when i run 98 the high octanes burn cooler than 91 and are more stable

[dmoney]

the 91 in this country really is crap and 95 not much better i reckon and prob not even close to the octane they say. 98 has gota be the best and worth the extra for peice of mind aye

[T-Thunder13]

sweet! cheers people! i cant ride at the mo any way got a fractured heel, so doin a bit of maintenence while im off work. so on to 98 it is.

[zadok]

You said it at the beginning of your post "never had any running problems".
Personally, unless I was having problems or the manufacturer specified a higher octane, I'd rather keep the extra money in my pocket.
I tried the higher octane in my previous two bikes and it didn't make it go any better.
If you want this supposed 'peace of mind' and got money to burn (quite literally), go for it.