Just a quick question

[zooman]

Hi my name is shadow.

I am new to this forum and bikes in general. I just have a quick question for any of the regulars with knowledge of ninja 250r's.

I owned a 2010 ninja 250r for 6months which was the first bike I owned and rode. I bought it as a demo with 300kms on it. I kept it completely standard. Recently I sold it and bought a 2012 ninja 250r brand new.

Right from the start I noticed a difference between the two bikes. most noticeably, when doing 100km/hr the old bike ran at 7500rpm. at the same speed the new one sits at 8500rpm. The new bike is more fun to ride and seems to have more acceleration/power when accelerating from 8000 to redline. However, it seems to use more fuel. Also, the new bike idles much easier and higher rpm. for example when started with choke on it jumps straight to 4000rpm. I have to adjust the choke straight away to get it back under 3000rpm.

Today i had my first service done (bike has done 1200kms). After picking the bike up it is running very similar to my first ninja - ie sitting at 7500rpm when doing 100kms and idleing at lower rpm. I phoned the mechanic to ask what he adjusted and he said the only thing that has changed is the bike is now running thicker oil (recommended by kawasaki) as opposed to the factory oil which is thinner and he also put 10psi more tyre pressure in both tyres. Could this really account for the difference in rpm?

I have asked a few people I know what they think and they said that the rpm at a particular speed can't change unless the cogs are altered. Is this true?

Sorry for such a silly question but i am really confused. I prefered the bike when it was running slightly higher rpm even though it was using more fuel. It just seemed to accelerate better at higher rpm.

[Alex]

The tachs just aren't that accurate. With the same gearing and same tires, the engine would need to be turning the exact same speed for the same road speed across both bikes.

[zooman]

So, either i am losing my mind or something that was done at the service caused the tacho to read differently and bike to idle differently?

[zooman]

by the way, thanks for the reply alex. sorry i am such a noob!

[Alex]

Idle differently is probably because he adjusted the idle knob back to spec, and 10 psi low in the tires would cause the revs to drop slightly at speed once they are aired up to spec. But no, there's nothing they could have done that would have actually made the bike's engine turn 1000 rpm lower at speed.

(P.S. Check your tire pressures much more often, running 10 psi low is not just a bad idea, it's truly dangerous)

[zooman]

I did ask him about idle knob. he said he didnt touch it. He did say there was a small oil leak which he fixed by tightening a clamp but doubt that affected anything. the bike was so different at low rpm that when I first took off the bike began to stall straight away so I tried to give it more gas to prevent this from happening and there just was no power at all.

I will take it for a ride tomorrow and see how it is going.

[Motofool]

Could it be that your first bike had a modification done to the sprockets?

Changing the front sprocket to more teeth for reducing rpm's at high speeds is a common modification.

Did your mechanic adjust play of the clutch lever?
If rpm's changed 1000 (8500 to 7500) at same bike speed (100 km/h), the clutch was slipping before for bad adjustment or bad oil.

[zooman]

Originally Posted by Motofool

Could it be that your first bike had a modification done to the sprockets?

Changing the front sprocket to more teeth for reducing rpm's at high speeds is a common modification.

Did your mechanic adjust play of the clutch lever?
If rpm's changed 1000 (8500 to 7500) at same bike speed (100 km/h), the clutch was slipping before for bad adjustment or bad oil.

Would you be kind enough to elaborate on what you mean when you say, "the clutch was slipping before for bad adjustment or bad oil."

The mechanic said that there was an oil leak of some kind which he fixed by tightening something. Could this have been related to slipping clutch? Would I have noticed a slipping clutch while riding the motorcycle for 1200kms before having the bike serviced?

Thanks

[Motofool]

Yes, the clutch must have been slipping during the time the engine's rpm's were higher.

I say that because there is a solid transmission from the crankshaft to the rear wheel.
The only flexible transmission rate is introduced by the clutch.

When the clutch is commanded to function, their multiple friction discs start an in-oil-slip that allows the transmission aft that point to slow down respect to the rpm's of the crankshaft (on which end the clutch is installed).

The conditions that I mentioned make some little slip among the discs happen when the clutch is not commanded to engage.

Check this link:
http://www.dansmc.com/clutches.htm

[zooman]

Originally Posted by Motofool

Yes, the clutch must have been slipping during the time the engine's rpm's were higher.

I say that because there is a solid transmission from the crankshaft to the rear wheel.
The only flexible transmission rate is introduced by the clutch.

When the clutch is commanded to function, their multiple friction discs start an in-oil-slip that allows the transmission aft that point to slow down respect to the rpm's of the crankshaft (on which end the clutch is installed).

The conditions that I mentioned make some little slip among the discs happen when the clutch is not commanded to engage.

Check this link:
http://www.dansmc.com/clutches.htm

Thanks heaps for the reply Motofool. So to summarise, before my bike was serviced it had a slight slip in the clutch which I noticed when doing 100km/h due to my bike producing a higher than normal rpm at that speed and at idle.

After first service, the fixing of a small oil leak or tightening of certain clamps/parts has corrected this which has changed idle and rpm at 100km/h. Now my bike is running as it should which is exactly like my first 250r.

does that make sense?

[Alex]

No, sorry, it doesn't. A slipping clutch doesn't cause a bike (or any vehicle) to have its engine run a stable percentage higher, that when fixed runs lower. If it was slipping under throttle, it would show quite variable revs, even at the same road speed.

[zooman]

Originally Posted by Alex

No, sorry, it doesn't. A slipping clutch doesn't cause a bike (or any vehicle) to have its engine run a stable percentage higher, that when fixed runs lower. If it was slipping under throttle, it would show quite variable revs, even at the same road speed.

Ok, no problems. I really appreciate you guys trying to solve this one. I am not a silly guy and was pretty sure that when I posted the question here it was unlikely anyone would be able to give me an answer. I know a lot of people who have solid knowledge of bikes who have pretty much told me I am dreaming.

However, I know that I am not and that something has changed. Was really hoping the slipping clutch thing was the explanation. I am sure the bike is as it should be now. It's just my personality to sought an explanation as to why it wasnt previous to my service.

Ride safe and all the best, shadow.

[Alex]

Heck, no worries! We're as eager to figure out what might be causing it as you are. I didn't want to bring this one up as it's unlikely, but it's another cause for the tach behaving a little strangely:

http://www.ninjette.org/wiki/Ignitor_problem