What Octane?

[Amz]

I've got a XL250 with the water cooled NX250 DOHC engine in it which apparently has a 11:1 compression ratio. Which octane fuel should I run in it - 91 or 96? It tends to knock a little if I go around roundabouts etc with out changing down enough (hard to know which gear I'm in as just gone for 2 stroke to 4 and 4 gears to 6) and a tend to cruise around a lot in 5th and 6th (on the open) and commute a lot a hilly stuff. I've been running 91. I know I should probably just throttle off and change down and I do but sometimes I cruise through an intersection or something and open the tap a little and it doesn't like it much. Would I be better to mix in some 96 occasionally or go straight 96 or just get my crap together and ride like a noisy b/tard with it's mod'd pipe.

[merv]

Try 95 (you can't get 96 these days) straight, and it should be sweet, and flipping heck change down some gears when you should be. Keep it above about 3,000rpm if you can.

[TimeOut]

Go for 95+ if you're getting engine knock it's doing damage.

[Amz]

Right, ok! It doesn't have a rev counter so I don't really know what's going on, having come from a 125cc 2 stroker but I get your drift. It's smoother with a few revs on so I'll ride it on its sweet spot. So 95 can't hurt then?

[TimeOut]

95 won't hurt the bike just the pocket.

[merv]

So 95 can't hurt then?

Nah, those bikes have been around long before you could get 98 in NZ so 95 will be fine.

[Griffin]

Nah, those bikes have been around long before you could get 98 in NZ so 95 will be fine.

Wot 'e said

[CookMySock]

if its knocking at low revvs it WILL be knocking at high revvs and high load, even though your ear can't detect it (well you sorta can - sounds like a tray of glasses rattling, hard to hear.) The low rpm knock wont really do damage (unless its horrendously baad) but the high speed one will break rings, crack pistons, burn tips off sparkplugs, burn valves etc etc.

Bottom line, if its knocking AT ALL then you can't ride it more than half throttle and half revvs anywhere, and certainly you should not be climbing big hills at large throttle settings at any rpm.

I wonder if high octane is actually cheaper to run, as I get much better range on it. 280 vs 350km.

DB

[AllanB]

I'd say the 'knocking' noise has nothing to do with fuel and more the engine being laboured clanking around trying to pull the bike and you in too high a gear. Does it go when you get a bit of speed up in he same gear out of that roundabout?

Change down. Give it a few revs.

95 will be fine.

[koba]

I know I should probably just throttle off and change down and I do...

Thats pretty much all that needs to be said really, and you already said it!

[nico]

slightly changing the subject, but what do you guys run in your bikes? and why? im running 91 in my vfr but thinking i should try 95+ for a couple tanks any real benefits?

[AllanB]

I was told to run when I purchased my Hornet new, I tried a tank of 95 and I did not notice any difference so stick with 91. Several others I know have done the same. Your owners handbook will have a minimum octane rating listed.
It does depend on the bike.

[CookMySock]

I can run any octane fuel - I cannot tell the difference in performance. I get 270k ish out of 91 and 360k ish out of 95/96.

DB

[xwhatsit]

The NX250 engine is not the sort of thumping grunter you can lug everywhere; it's a fairly revvy high-output single. I'd be suprised if that knock is actual detonation/pinking, much more likely to just be the sort of hideous noises these singles make when you try lugging them like that. It'll shudder and shake and the chain will just about jump off the sprockets.

Nothing to worry about -- you've got 6 gears for a reason, have to keep it on the boil a bit. Not like a smooth two-stroke or inline four, it won't pull from idle without protesting.

[stevewederell]

How about a 1998 CB600 ? I've been running her on 91 but have just discovered the plugs are black and gritty.
I've only had her for a few months so I may have just bought an already dirty lemon.