ZXR250 issues

[High_Voltage]

Hey i have a 91 zxr250c and just having some issues with it.
at the moment when i throttle it back when its warm its doesnt accelerate like normal. it seem a bit sluggish. I had the same problem before and i took it into the bike shop and got the carbies tuned and cleaned and the fuel system cleared and new plugs and now the problems come back
it has cut out a couple of times on me on the motorway too
could any1 give me some clues on whats going on and if its worth taking in2 another bike shop?
the on i took it into originaly has closed down recently so cant go back too them

[Sidewinder]

Hey i have a 91 zxr250c and just having some issues with it.
at the moment when i throttle it back when its warm its doesnt accelerate like normal. it seem a bit sluggish. I had the same problem before and i took it into the bike shop and got the carbies tuned and cleaned and the fuel system cleared and new plugs and now the problems come back
it has cut out a couple of times on me on the motorway too
could any1 give me some clues on whats going on and if its worth taking in2 another bike shop?
the on i took it into originaly has closed down recently so cant go back too them

new bike time!

[iamkirk]

What fuel you using? Should be running it on 91.. Hope you haven't made the same mistake a lot of people make (including myself once) by running it on 98.

[High_Voltage]

new bike time!

i was hoping to keep this bike until i can get something bigger

What fuel you using? Should be running it on 91.. Hope you haven't made the same mistake a lot of people make (including myself once) by running it on 98.

yea could give it a go but i have been running it on 95 and it has been fine for a while tho

[Slyer]

Why 91?
There's no harm in higher octanes.

[SS90]

Quite a common problem with 4 cylinder 4 stroke 250's is the carb slide needles.

These needles, control the fuel your engine gets above idle (idle jets), and below full throttle (main jets)

Basically, there is more to it than that, but that's a basic explanation.

Now, as your ZXR is getting a little older, and a few K's have been racked up, of you think about it, every time you accelerate and decelerate, the slide needles go up and down in the emulsion tubes...this creates wear on both the emulsion tubes, as well as the needles.

after a few years, they wear out significantly, and they are unable to meter the fuel your engine gets correctly, and will supply more fuel than it needs (the needles get thinner, the emulsion tubes get bigger, meaniing more fuel goes into the throttle body.

You will have to strip the carbs and remove the needles and emulsion tubes to check this, although the wear can sometimes be hard to see.

the symptom of running sluggish when hot would indicate this is your problem.

[xwhatsit]

Why 91?
There's no harm in higher octanes.

There is on older engines designed for lower octanes. Higher octane fuels burn slower. My 250RS fucks about and spits and farts just off idle with 98, bloke I know with an SR500 complains about the same thing. No `harm' as such but it certainly doesn't seem to play nice with the carburettion. Maybe on a perfectly set-up unworn engine it wouldn't be an issue.

Now, as your ZXR is getting a little older, and a few K's have been racked up, of you think about it, every time you accelerate and decelerate, the slide needles go up and down in the emulsion tubes...this creates wear on both the emulsion tubes, as well as the needles.

You're probably right there, especially CV carbs, the needle vibrating up and down constantly with the vacuum even at constant throttle. But the fact he says it's not normally like this, and how it cut out on the motorway... could it be fuel flow problems? Not enough fuel getting to the float bowls, especially at high RPM (on the motorway, cutting out) and when it's warm it's not getting enough fuel...?

[SS90]

T
especially CV carbs, the needle vibrating up and down constantly with the vacuum even at constant throttle. But the fact he says it's not normally like this, and how it cut out on the motorway... could it be fuel flow problems? Not enough fuel getting to the float bowls, especially at high RPM (on the motorway, cutting out) and when it's warm it's not getting enough fuel...?

Yea, that's a point, but it seems that it happens when it his hotter (I think I read that!), which (to me) would indicate that it is (perhaps) too rich.

My experience has been that (particularly in high revving 250 4 cylinder 4 strokes.....( think of how hard those needles are rattling at 17,000 RPM!) when the needles are worn, it seems to "flood the air box"

Maybe a quick test would be to go to a wrecker, see if you can buy the lid off an old 91 zxr 250 (they are different to the earlier ones, as are the carbs), drill a few holes in the top (of the worse of the two lids of course) and simply test ride it for a couple of days....if it improves operation, then it would be prudent to suspect the needles.

Also, just check that all the hoses going from the carb to the air box are connected up....in ZXR 250's, the float bowls of the carbs must be kept at the same pressure as the airbox (if the vent hoses from the bowls aren't connected to the top of the air box, this can cause the bike not to rev cleanly over 8000 RPM under load), but it's unlikely that is the problem, as likely he would have mentioned that!

I hope that wasn't too confusing!

[hayd3n]

when the carbs were cleaned was a fuel filter added????

[iamkirk]

Why 91?
There's no harm in higher octanes.

As it was said earlier, as far as i know these old IL4's were designed i think for 87 octane so anything above 91 shouldn't make a difference.

Its also because of the additives that petroleum companies put in 95 and 98 to raise the octance number that cause problems such as it dying on you., even caltex and their 'cleaning' additive will do this as it will pick up all the shit in your carbs and throw it into the neddles and so on..

I know a mechanic that worked at red baron for over 10 years and saw exactly what you described happening on a lot of bikes because they used 95 or especially 98.

Hope this works for ya.

[Brett]

As it was said earlier, as far as i know these old IL4's were designed i think for 87 octane so anything above 91 shouldn't make a difference.

Its also because of the additives that petroleum companies put in 95 and 98 to raise the octance number that cause problems such as it dying on you., even caltex and their 'cleaning' additive will do this as it will pick up all the shit in your carbs and throw it into the neddles and so on..

I know a mechanic that worked at red baron for over 10 years and saw exactly what you described happening on a lot of bikes because they used 95 or especially 98.

Hope this works for ya.

There may well be substance to this...

Just my experience, but I have had a few ZXR's and I used one in particular most of the time, clocking up 40,000kms on it...all on 98 or 95 octane and never once had any issues with it. That said, it is only one bike and itmay have been slightly differently tuned.

[steelestring]

I never had issues with running mine on 95 or 98 either....
but I have had a problem with dirty build ups when useing the reserve fuel line, especially if you never use the reserve tap very much and then turn it on during a longer trip... and then....boooooyaaaaaaa!!!! must have filled the pants of my fuel filter!!! Slugish behaviour.....