ZXR250 losing power

[tone_crafter]

I have a 1989 ZXR250A. Lately I've been finding that when I wind the throttle on once the revs get up past about 12,000RPM the revs scream off and the bike losses power as if it were in neutral. Seems to be worse the faster I wind on the throttle. If I wind it on really slowly it seems to hold ok.

Thought it could be the clutch slipping but wouldn't that happen at lower revs when the engine is producing the greatest torque? Could it be the gears not engaging properly?

The bike red-lines at 19,000RPM and there's no limiter so I know its not that.

As you can probably tell I'm not much of a mechanic so any ideas would be greatly appreciated.

[bungbung]

If the revs continue rising past 12k and the road speed remains static or decreases, then it will be your clutch slipping.
12k is where the power begins on a zxr

[xwhatsit]

Sure sounds like clutch slipping. Your engine won't be producing greatest torque at low rpm -- it will increase over the rev range (especially on a four-banger) and then begin tail off, probably around 12-14,000rpm considering a 20,000rpm red-line. I'm a empty-headed fool, but I would've thought it'd be horsepower (i.e. lots of work in a short period of time) that would cause clutch slippage.

It could be the clutch cable is incorrectly adjusted. It might've been slipping slightly for a while because of the cable being too tight, and now it's getting worse because the clutch is wearing out fast. On the clutch lever there's a little twirly nut with a locknut on the outside of the cable, just like on a bicycle's brake lever. Back it off a bit (turn it in, clockwise) and see if that makes things better.

If there's no more adjustment left at the clutch lever, you can adjust it at the engine side. The method varies from bike to bike, but it'll probably just be a pair of locknuts.

If you run out of adjustment completely, or you find no matter how you adjust it the clutch is either slipping or dragging, then the clutch fibre plates are probably worn out and you'll need to do them.

[HDTboy]

It's your clutch slipping.
If you want guidance to do it yourself, buy a set of fibres, and bring it to me.
My number is 0212517356

[tone_crafter]

Thanks for the offer. I'll try adjusting the cable first and see if that makes a difference. If not is a set fibres expensive?

[HDTboy]

Ring Spectrum and ask

[Mikkel]

I had my clutch slipping as well. I had them replace my clutch springs and rebuild the clutch. Helped heaps! Sounds like that is indeed what is wrong with it.

What engine oil are you using? That can be quite important! If you use an oil with friction modifiers that can fuck the clutch in which case you need to drain the sump, change your filters, rebuild the clutch and get some proper oil.

How many kilometers has it done btw?

And btw - there is a rev limiter at approximately 19k RPM. When I'm caning it I usually up-shift at 18,5k. That's the optimal since it drops down to about 14k RPM where the torque curve peaks. Maximum power is delivered at 16,5k RPM. They're lovely little bikes.

Alternatively - check your inline fuel filter. That can cause weirdness at higher revs if it's been partially blocked.

[tone_crafter]

I had my clutch slipping as well. I had them replace my clutch springs and rebuild the clutch. Helped heaps! Sounds like that is indeed what is wrong with it.

And btw - there is a rev limiter at approximately 19k RPM. When I'm caning it I usually up-shift at 18,5k. That's the optimal since it drops down to about 14k RPM where the torque curve peaks. Maximum power is delivered at 16,5k RPM. They're lovely little bikes.

Alternatively - check your inline fuel filter. That can cause weirdness at higher revs if it's been partially blocked.

Just changed my fuel filter a few weeks ago so that could be the problem. Can u remember how much it cost to rebuilt the clutch? It doesn't help that my tacho is stuffed as well. Makes it hard to know exactly how many revs im doing. It works fine most of the time but sometimes jumps up to about 10kRPM and reads smoothly from there. This means if I'm actually doing 10k the needle is off the gauge. Havn't gotten around to fixing that either yet. Little short on money as I also need to replace the rear tyre soon. Ahhhhh well tis life.

[Mikkel]

Just changed my fuel filter a few weeks ago so that could be the problem.

Unless you turned it upside down I think we can conclude that the fuel filter is not the issue.

Can u remember how much it cost to rebuilt the clutch? It doesn't help that my tacho is stuffed as well. Makes it hard to know exactly how many revs im doing. It works fine most of the time but sometimes jumps up to about 10kRPM and reads smoothly from there. This means if I'm actually doing 10k the needle is off the gauge. Havn't gotten around to fixing that either yet. Little short on money as I also need to replace the rear tyre soon. Ahhhhh well tis life.

Sorry, can't remember. I had it done over a couple of workshop visits and I wasn't charged labour for rebuilding the clutch since the mechanic said he should have picked up on the steel and fibres being shot when he was in there to change the springs anyway...

Get your tacho fixed mate - it's the most important readout you have, not counting the idiotlights.

And yes, tyres get expensive...

[CookMySock]

If you want guidance to do it yourself, buy a set of fibres, and bring it to me. My number is ...

gee what a helpful bloke. Good on ya mate, thats the sort of thing I like doing too.. cheers

DB

[tone_crafter]

Ok I loosened up the clutch cable and it seems to be fine now so hopefully the clutch is ok. I don't really like the cable design on this bike. It has a tight metal bend in it at the lever end and then changes to the plastic covering after the bend. The part where the plastic covering joins with the metal bend can actually come out of the metal causing the cable to tighten up. Hard to explain without a photo. May need a new cable.

On a side note would anyone have any idea what could cause the tacho to play up? I don't want to get a new tacho then find its the sensor thats causing the problems.